In my experience you don't need to remove SIMBL to get Safari working again
I experienced exactly the same crash-on-launch symptons as DEJMAC following the 2013-001 Security Update. Chances are, you have SafariStand 5.1.182 installed.
You need to either remove "SafariStand.bundle" from ~/Library/Application Support/SIMBL/Plugins/
...or just update it.
You can get SafariStand5.1.183 from http://hetima.com/safari/stand-e.html
This version works fine with Safari 5.1.8 and I love it!
Use Get Info to check the version (click on the file and press Cmd+I)
There is nothing fundamentally wrong with SIMBL or Safari Stand in my opinion (based on my own experience), however, the latest security updates have tinkered under the hood of safari (outdated flash plugins are now disabled automatically for example) so this kind of glitch is inevitable but it does not fundamentally undermine the concept of SIMBL as has been suggested.
I have several SIMBL plugins running under Snow Leopard 10.6.8 and have no problems. The latest SafariStand for SL works just fine with Safari 5.1.8
For instructions, see my post in https://discussions.apple.com/thread/4890746