If you're like me and make very complex projects like MMORPGS and such, you might find yourself going over 10-30,000 lines of code. After about 25,000 lines of code, you'll notice 1 or more seconds of type lag between letters you press. This is highly annoying.
So here are my tips to avoid type lag:
1) If Flashbuilder has been running for more than 1 or 2 days, quit and restart it. Flashbuilder gets slower and slower the longer it run. This is fixed with a quick restart
2) Edit your files in text mode- right click->Open With->Text Editor. Even my 30,000 line file has no type lag anymore now that I discovered this.