If you have access to a PC (or Virtual PC), you can do a backup, then do a restore after upgrading.
However, this
doesn't back up SMS text messages. I still haven't figured out why, or where they are kept (probably because I haven't looked that hard).
But it's worth noting, as I was
very pissed off after losing months of text messages, even after doing backup and restore
Other than that though, its well worth doing the upgrade.