It seems like Safari 3.0.2 is much better behaved, so far, for me in this regard, than 2.x was. Although, others have reported that it seems to have more memory leaks. It seems to be worst in usage profiles like mine -- lots of tabs open at any given time, and several tabs that are re-used with lots of page loads -- particularly if I've got a couple of webmail pages open in tabs.
But again, so far, with Safari 3, I seem to be doing a lot better. Although, after having Safari 3 for a day or two, I got a RAM upgrade as well, which helps probably quite a bit more than Safari does.
EDIT: I did notice, after about a day of having Safari open and doing stuff in it, that my free memory had started to tank and I got pageouts. I had about 30 MB free memory and had accrued a small number of pageouts (207), but they were going up doing minor stuff. I quit Safari and re-opened it, and immediately re-opened the same tabs, and with just that one change (all other software still running), I got back up to 350MB free memory. That suggests to me that the leaking is actually still quite an issue.... This is without even resetting it or clearing the cache.