Disclaimer: This is my first Android device. I dont know what a normal amount of UI lag is for a smartphone. That being said, I've heard people acclaim the Galaxy S line as being a highly advanced piece of hardware and I think what's going on in my phone is a bit unusual.
Symptoms: The phone lags during a variety of operations. Coming from the lock screen, the display stutters (rather than zooming in smoothly), changing between screens there's a sticky lag. Coming out of any phone menu back out to the home screen is very jerky.
Basically, almost any transition animation is laggy/jerky/hangy/sticky/whatever. Both my girlfriend and my mom have this phone and neither of them hang as much as mine.
Here's a list changes I'm running:
LauncherPro(full), the google search widget from these forums, Weather and toggle, Advanced Task Killer, and a smattering of apps that arent interface related.
The only reason I'm concerned is because the laggyness seems to have gotten a little worse over time. Is there a way to troubleshoot to see if I've got a resource hog slowing me down?
Personally I would recommend both rooting and removing (moving) all of the bloatware programs from your phone. I too had this problem at times and now after doing both the root and crap removal it is running a lot smoother.
Not to start a controversy, but get rid of the task killer and reboot the phone. Also, if you are running LP, make sure you delete all the widgets and unused screes from the TouchWiz interface, then restart LauncherPro.