Some folk are saying that disabling all the Spotlight Search options speeds up the 3G running iOS4 (after 2 hard resets, that is). Since I never use spotlight search on my phone, I'm giving it a try:

Launch the Settings app, go to General::Spotlight Search and deselect indexing for all or as many items as you want.

For me, after 2 hard resets, apps launch noticeably faster on first launch, and also switch faster when using task switching. Makes me a bit firmer in my resolve not to replace my 3G until it stops working.
If it's brokenless, don't suffix it...