Mat posted about Safari 3 Adblock earlier this week. To me, the most impressive feature of that plug-in is its support for Adblock Plus filter subscriptions. In that same vein, SafariBlock, a program TUAW has covered in the past has received a significant update. In version 2.0, not only is the plug-in now open souce, but it is also compatible with AdBlock Plus subscriptions! It's Leopard compatibility has been improved from version 1.3.1 as well. I had some trouble getting SafariBlock 2 installed (the installer and a manual installation gave me errors), but the plug-in ended up working just fine.
Having played around with both plug-ins, I think that they both have their pros and cons. While SafariAdblock seems to be a little bit better at distinguishing between ad and non-ad flash videos (SafariBlock automatically whites out some video windows that are actual content, even if they appear near an ad header), SafariBlock is much better at working with web forms and sites that need to launch an action in either another window or in some sort of pop-up.
In any event, AdBlock Plus filter support has instantly transformed my Safari experience - bringing one of my favorite Firefox features to a browser that tends to be more stable on my system. Plus, SafariBlock is free - and I'm a big fan of free.