This tip from Macintouch reader Peter Chin in the Safari 1.2 report is a winner:

Feb. 9, 2004

Safari 1.2 update released

Peter Chin
I have observed that sometimes while surfing with Safari my CPU usage jumps to and sustains 100% (even when idle!) and scrolling is sluggish, especially while browsing UBBS and similar HTTP-based forums. I also noticed that entering text in those forums and in web-based email pages was painfully slow. Thinking that this could be similar to the problems with Sherlock and Adobe Reader, where there were too many enabled languages and/or plugins loaded, I did a Get Info on Safari and went to the Languages window and found all of the languages enabled.

So, I unchecked all languages except English, closed the Get Info window, and launched Safari. What a difference! Now scrolling seems back to what it was and my CPU usage idles back to the usual 15-20% when idle in Safari.

It definitely helped me out on my 3-year-old PowerBook G4/500. I suspect this problem is only noticeable on older, slower Macs and on web pages that support multiple languages. Prior to coming across this tip, I suspected Safari was the problem after trying to investigate by opening up 2 terminal windows and running tcpflow in one and the top -u command in the other. top revealed high CPU usage whenever my machine seemed to stall or hang as it never did before.