Could happen but most of the active builders can quickly throw out a new version. Some do it daily! Security is not really an issue but of course you cant be 100% sure what is added or not included. You can run into some strange bugs here and there but that will be it and probably documented by builder already. I believe it is quite easy to make your own build, can be done with free tools.
http://developer.mozilla.org/en/docs/Build_Documentation#Build_and_Install almost equals waste of time for me - way too much work for too little gain. Having said that Stipe builds were repeatedly faster in benchmarks than official build when I used it, 1.5.0.1 or something. He uses some of the rare original contribution, patches from Mmoy - see forum again, I can say much more about details. My impression is a few have tried to optimize and truely tried to make a difference and many more want to make their "own" build... How internet is
Not worth a headline when it comes down to real browsing. Flock and K-Meleon are real alternatives.