I've long believed there's no such thing as "too many pixels." My desk setup follows that to a tee: I currently use a 27-inch iMac and two external displays, which, when combined, offer me 6656 horizontal pixels of resolution. But this setup, while great, requires a fair bit of head movement--it's over four feet from the left edge of the left display to the right edge of the right display.
Because of this, I'd recently been mulling over 4K displays: They offer many more pixels per inch than your traditional monitor, allowing you to have lots of screen real estate at your disposal without having to fill your desk's horizontal space with screens. Making such a move can be a pricey proposition, however; even the least-expensive 4K displays are $500 to $600.
But then a helpful friend alerted me to a deal on the Seiki SE39UY04, a 39-inch Ultra HD TV set with 3840-by-2160 resolution. Amazon has these sets for just $339, and at that price, I thought I'd give it a try.
Not for all Macs
Before you run off and order a 4K/Ultra HD display of your own, you first need to know if your Mac will support said 4K display. Checking your Mac's technical specs on Apple's website provides the official answer: only the Retina MacBook Pros and Mac Pro are listed as supporting 4K displays. (The MacBook Air and iMac will drive an external display at up to 2560x1600; the Mac mini's limits aren't listed, but it's got an older video card than the iMac, so it's doubtful it can drive a 4K display.)
As I have a 13-inch Retina MacBook Pro, I went ahead and ordered the Seiki TV set. In addition to the TV, I also ordered a mini DisplayPort to HDMI adapter; this adapter is required to get the full 4K resolution from your TV to your Mac.
There are many of these adapters out there, and most any one should work fine. I used this one from Monoprice.com.
With the TV and adapter in-house, initial setup is relatively simple. Plug in the TV, connect the HDMI cable to the adapter, then connect the adapter to your Mac.
Once everything was powered on, I found I had to do some adjusting to the TV's settings: it ships with noise reduction on (I disabled it), and with sharpness and brightness values at 50 (I set them both to zero, and increased the contrast). With these changes, I found the image quite nice--text is sharp and colors (after a few tweaks to color settings) look good.
For fun, I also tried connecting the display to my 2011-era iMac, and it worked...occasionally. Sometimes when I'd connect, I'd see the full 4K display; other times, I'd see a blue screen on the TV and "no signal." I wasn't able to ever make it work reliably, so I'd say if you have an older computer that doesn't officially support 4K displays, this setup isn't recommended.
The inexepensive TV I chose will only run at 30Hz at its native 3840x2160 resolution; more expensive sets will run at 60Hz. However, that 30Hz is also the highest level at which the 13" Retina MacBook Pro will drive a 4K display, so I wouldn't do any better with a more expensive monitor. (The Mac Pro and 15" Retina MacBook Pro can run certain DisplayPort 4K displays at 60Hz, via multi-stream transport.)
While a 30Hz refresh rate is fine for mostly-static images (like windows and text and photos), it's not ideal for video; fast-action videos (and video games) will exhibit some ghosting/shadowing. Some people find these issues more distracting than do others; for me, they're notable enough that I wouldn't plan on watching a feature-length movie at the 4K resolution setting, though I had no trouble with shorter YouTube clips.
Putting it to use
So how does one use a massive 39-inch TV as a display? In my case, I've put it at the back edge of my desk, about three feet from my eyeballs. It works well at that distance, though if I had a different office layout, I'd consider wall mounting it to move it back a bit further, and allow up/down angle adjustments. I put my Retina MacBook Pro on the desk in front of the massive screen, and it's small enough that its screen doesn't visually intrude on my view.
As for how I'm actually using it on a daily basis...I can tell you it's not as seen in this screenshot.
Instead, this is simply to demonstrate what's possible in that number of pixels: six 1024x768 browser windows, a BBEdit document window, a Finder window, and then Mail, Maps, and Calendar along the bottom of the screen. That's an incredible amount of information on one display.
So that's the theoretical; what about the actual? In my day-to-day work, email is critically important to me (as it's our customers' primary method of interaction). As such, I've devoted the left third of the screen to a huge Mail window (in OS X's Classic view). This lets me see about 35 one-line summary emails, along with a preview pane that's large enough even for truly epic-length messages.
To the right, I keep my "accessory" apps, such as my Twitter client, Messages, a small BusyCal window, and some floating widgets (which I float above all via this ancient Mac OS X Hints tip). When I need to edit a graphic, or work in Excel or Pages or some other "big" app, I'll open it in this section on the big display, sizing it as needed for the project--if I need the pixels, I'll cover Mail and everything else, but generally, I try to keep Mail visible at all times.
The downsides of massiveness
If you're not used to big and/or multiple displays, you may find the required head movements tiring. For me, though, I'm doing much less moving about, as my pixels are now much closer together horizontally. The Seiki comes on a fixed stand; you can't adjust tilt or swivel without pivoting the entire set. I found the fixed angle fine on my desk, but a wall mount would provide more flexibility.
Big screens do make it easy to lose the cursor, however; you'll probably want to use a tool like Mouseposé or similar that lets you call out the cursor's location via a hot key. I regularly lose track of where my cursor is hiding amongst all those pixels.
And while we're on mouse-related items, a big screen requires lots of cursor movement: Getting from one side to the other takes about three swipes of my trackpad. This can get tiring after a while; I find myself using keyboard shortcuts whenever I can, as well as switching directly to the window I wish to access, either via the Dock's contextual menus or via our own window switching utility, Witch.
The last word
Super-large monitors aren't for everyone--honestly, I'm not sure this one's for me yet. I've been using it for several weeks, and while I like it a lot, it does take up a lot of my desk (both horizontally and vertically). But for the price, if you've got a Mac that can use it and need for more screen real estate, it's a relatively cheap way to add a massive amount of pixels to your setup.