Galaxy S Captivate - slow at times

Well, Android is a multitasking OS so it's highly possible to have too many things going on at the same time, causing things to run slow or even freeze altogether.

For best performance, I'd disable auto-sync, network connection, as well as auto-run apps such as weather/facebook/yahoo, live wallpaper etc, in fact if you can do without these apps - just use the web version from your browser and uninstall the apps/widgets on your phone. I also suggest you check your ram usage from time to time via the built-in program monitor widget (which also allows acts as a task killer/ram manager).

Of course, its really up to you where you want to be in the pretty/convenient vs. performance scale. I personally like things to be quick so I have my phone set up like what's stated above.