I jailbroke my 3GS the same day I got it, and I had it for a year. I then upgraded to 4 half a year ago and it's not been jailbroken since. I think it would be a proper time to do so now if Siri will be succesfully ported for the 4...
I happen to like iOS 5 and I felt the same way about iOS 4. Until there is a specific reason I need to jailbreak then I won't do so, the App Store always has the app that I need available.