Wirelessly posted (iPhone 3G (white): Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_2_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5H11 Safari/525.20)
I found my iPhone 3G to be pretty sluggish when I had Winterboard installed (because WB consumes such a large amount of available RAM) but even after uninstalling it, MobileSubstrate and Notifier, it still felt slow. I just restored to 2.2.1 or whatever the hell the new one is - un-jailbroken - and everything seems much more responsive. YYMV.