- The backups can take anywhere from 30 minutes to 4 hours.
- The backups are not “incremental,” i.e. they backup all the data on the phone.
- If someone calls you, the backup is interrupted.
- Whenever the backup is cancelled or interrupted — when, y’know, have to use the phone — that backup data set is corrupted.
I have several (more than 30) applications installed in my iPhone 2.0 (some of them are over 10MB). I’ve been a bit disappointed with the oh-so-slow syncs in iTunes due to the required backup process. Searching a bit, I found that I could disable the backups by setting a hidden iTunes preference. Quit iTunes, open Terminal, and enter this command:
defaults write com.apple.itunes DeviceBackupsDisabled -bool YES
From the comments:
Also check out the free Backup Disabler, which is probably just a GUI for this hint.
UPDATE: iPhone firmware 2.0.1 dramatically sped up my backups! Yaaaaaaaay! We’ll see if it fixes the other stuff. In brief testing, the phone feels less crashy.
UPDATE: The backups got slower again after I started accumulating a lot of third-party data on the phone again.
UPDATE: iPhone firmware 2.1 is waaaaaaaaaaay faster on backups, and on installing apps.
jjmarcus tech solutions 
jonathan: so are you just going without backups then? or turning it on & off periodically?
Since finding out about this, I enable backups right before I go to sleep, and let it run while I sleep — and while people likely won’t be calling me. Then I disable them in the morning.The disturbing thing is that my phone is clearly really screwed up. I’m hopefully getting it replaced tomorrow at the Apple Store. I’ve restored it to defaults now like 7 times, and each time I try to restore from what I thought was a good full backup, it turns out the backup is incomplete.I’m disgusted with this whole scene, with backups and with the terrible application updates and management mechanisms.
i *think* the just-now-released 2.0.1 fixes this. not totally sure, but my phone seemed to do better after installing it.