Firstly, read Apple’s FAQ

To initiate a backup (these are by default automatically done regularly but sometimes you want to do one anyway), right click on the iPhone in iTunes and click “Back Up”

Essentially, the iPhone backups are stored in a compressed SQLLite format on your HDD (on mac, /Users/yourusername/Library/Application Support/MobileSync/Backup/). So if you want to backup your backups, backup that directory. It’s in your home directory, so Time Machine will normally grab it unless manually excluded.

Now if you’re a developer or just a curious individual, you may want to peek inside those files or extract the data manually. This is quite possible because they are just SQLLite data files. Check out this awesome iPhone backup extraction software for mac. Be sure to send this guy a few bucks as a thank you. You can also do it the old fashioned way with a perl script. I found the perl script however didn’t convert all of my backup.

Actually modifying the data and sticking it back on the iPhone however I don’t believe is possible as it cryptographically signed to protect integrity (which is good for us developers).

Remember as a developer you chose to store files in the users “Documents” or “Cache” directory. Be nice and put anything that doesn’t really matter in the “Cache” directory to save the user’s backup time when syncing with iTunes.

KeepVid – Lets you download iPhone compatiable (and high quality) MP4 files direct from YouTube – just wack the YouTube URL in the box and you’re done. Thanks Pete.

MPEG StreamClip – it’s not often you find a useful and free video tool – but this is one. Drag-drop, convert to MP4 and click “iTunes” for one of the iTunes presets. Pretty straight forward. Mac only.