I've been looking around for a 64 bit safari adblocker and found one that uses the same firefox adblock subscriptions (so autoupdate is possible). The only drawback I see is you have to install SIMBL.
I've been using GlimmerBlocker. It runs independently of Safari so it's not affected by Safari updates or if it's in 32 or 64 bit mode.
Also, it has a few handy functions that perform sort of like Greasemonkey and Stylish for Firefox, which I love--I use it to remove needless columns on Facebook and YouTube =D.