I have a problem with Safari freezing up for long periods of time, with the color wheel spinning while the curser is over the Safari window. When I quit Safari and re-launch the App, everything is fine for hours, and then it repeats.
This started under 10.2, I think, and persists with 10.3.
How much RAM do you have installed on your Mac? The proper answer is probably not enough. . . but seriously, how much?