The latest official release version of Safari suffers from memory leak problems, which means that after several hours of surfing, the memory usage of Safari can go up to several hundred megabytes.
However, the Safari team is now releasing binaries of its Webkit nightly builds, and the latest builds seem to have largely fixed the issue. Even after a day of use of the Friday, October 14 Webkit build, the memory usage has stayed within reasonable amounts, mostly in sub-100 MB territory.
The gold-rimmed Webkit icon is rather fetching too. :)