I subscribed to iTunes match within days that it was available in Canada, and went through the pain of uploading roughly 10 GB of independent-labeled CDs to Apple's servers. I know that by re-downloading music files, you can upgrade your matched songs to 256 Kbps AAC, but I haven't yet bothered doing so. Was it worth the trouble and cost?
Setting up you iOS device to iTunes Match turns off all non-music playlists, which annoys me since I often make playlists for podcasts (I ended up using to SpeedUp to make my own custom playlists:
http://itunes.apple.com/ca/app/speedup-player-pro/id385026296?l=fr&mt=8&ls=1 ). Apart from that, the experience is quite enjoyable, since you can "see", with album covers and so on, your entire music collection at once with no need for any iTunes syncing. You can press a button to download a song, album or playing, or you can simply start playing it and it will stream the songs as they are downloaded. It also works with another instance of iTunes, so for example from work I can see my entire collect, even though my songs are normally stored at home. Note that you can always redownload for free all the songs you already bought from iTunes, so this is mostly for people that are transitioning from a CD collection to something more "online".
Put simply, if you value "legally" upgrading your ripped songs to a higher bitrate, having an online music backup and access to your collection at all times, then the $30 a year is worth it. Those with spectacularly large collections (more that 25,000) or those that never rip CDs won't have much need for that service. After all, iTunes syncing, no matter how much many hate that process (and iTunes itself), still works fine for most of us.