The Cloud Player iPhone app has worked really well for me for the past couple months. Just recently it's been doing some annoying stuff where recently uploaded music doesn't show all the songs, and I have to delete them from the web player, recycle the library on the iPhone app, then restore them from the web player's trash, but everything about it has been miles ahead of what iTunes Match has offered other than matching.
And now that matching is available, I face the same double-edged sword I had before: I have lots of music I never, ever want to "upgrade" to the currently available remasters as they are really awful sounding. What remains to be seen at this point is if Amazon's matching system is smart enough to detect original, non-remastered music and leave it alone. So far, in the tiny, tiny fraction of my collection that it has upgraded, 440 songs so far, it hasn't picked up a single title that it shouldn't. It is, however, at just over 1% of my 38,500 songs.
Love having a metadata editor now! If they keep this up, there's going to be no reason to use iTunes.
iTunes Match's biggest problems for me have been chronic, painful slowness - taking 20 minutes to download one album is absolutely ridiculous - and mysteriously undownloadable songs. They're unforgivable sins - I don't have endless time and I can't deal with unavailable music. There's no solution to either problem, and Apple famously won't talk about issues, so Amazon has swooped in at the right time to collect the disgruntled like me.