iOS4 runs fine on my 3G. The longest part was deciding which app should go into what folder & what to call said folder.
I did a backup before I upgraded to iOS4 so it was much faster than some people who did a backup during the upgrade.
I think that's the secret. I plan on doing the backup before i upgrade my gf's 3G tomorrow.
lol... took me a while to decide what app goes in what folder and what they should be labeled.. OCD