Copy is good, sync works well. I'm up to 2.8TB of free space from referrals in one account of mine, and 600GB in another. In terms of free-for-life space (supposedly) that's pretty rad.
1. Their iOS app is a bit lacking. It can't play audio files in the background, so when you switch apps your music stops playing which is annoying. Dropbox for iOS continues streaming the music in the background.
2. It doesn't seem super fast, maybe because I only have a free account. I rarely see syncs top 1MB/sec, even though both computers I sync to regularly are on fast lines (100/10 for one of them, and 50/25 for the other). Still, it's free, so... (and to be fair: I've never closely looked at how fast dropbox xfers and I've largely replaced it with Copy).
Oh, here, my 5GB referral code (gives both of us 5GB). Let's see if I can get up to 1PB, shall we?