Reader Greg Decker has found the reason iTunes Match is taking so long to upload files. He writes:
I have a large iTunes library that I'm uploading to iTunes Match. I expected it to take awhile for my unmatched tracks to move from my Mac to the cloud but it's taking even longer than I expected and now I know why. My Mac is uploading audiobook files. I thought all of them were marked as such and wouldn't be uploaded, but apparently that's not the case. How can I keep these tracks from being uploaded?
Change the Media Kind tag
You'll need to change their Media Kind tag. To do that you must first turn off iTunes Match by going to the Store menu and choosing Turn Off iTunes Match. Don't worry, the files you've uploaded will remain in the cloud so you won't have to upload them again. Choose the Music entry in iTunes' Source list, select all the audiobook files in your music library, and press Command-I. Confirm that you do indeed want to edit information for multiple items by clicking Yes in the dialog box that appears.
In the Multiple Item Information window that appears click the Options tab. From the Media Kind pop-up menu choose Audiobook and click on the OK button. Your tracks will be moved into the Book playlist and won't therefore be uploaded when you next switch on iTunes Match. Go ahead and switch it on. iTunes will access your iTunes Match database and eventually pick up where it left off, but this time without those audiobook files.
You also might like to check out this handy guide if you're having iTunes Match scanning errors.
Fill in missing artwork now
While we're on the subject, I might suggest that to avoid this kind of problem everyone carefully scan through their iTunes libraries. You'll not only want to keep an eye peeled for errant audiobooks, voice memos, and podcasts, but also inconsistent tags. For example, in my collection I had one chunk of moptop music sorted under B for Beatles and another under T for The Beatles (because the artist sorting tag was incorrect). Also, if your album art is incomplete, choose Advanced -> Get Album Artwork in the hope that iTunes can fill in some of that missing artwork. If there are playlists that will make finding your music easier on an iOS device, create them now. And come up with a limited set of genre entries and assign those entries to your music so that you can better sort it later on other devices.