I've been playing with bookmarklets lately as I try to improve the one I created for our.imgSeek. During my struggles, I found a really useful online bookmarklet builder which is great for testing, formatting JS and compressing it (removing useless chars).
And why compressing it ? Firefox doesn't seem to care about your bookmarklet code size, but IE does and will silently ignore your code if it's longer than 500 chars. I'm feeling like an artist trying to squeeze useful code in 500 chars and trying a lot of hacks to overcome this IE limit.