I've recently given up on PrimalScript as my default AS editor, its been good while it lasted and its definitely a great tool for AS2.0 projects but over time some minor annoyances started to creep in. Particularly the difficulty in hooking it up to CVS or Subversion, lack of code folding and line wrapping really did my head in. Keith however blogged a little sneak-peek on PrimalScript 4.0 which looks very promising so I might well change my mind again later this summer. In any case, after trying a few other obvious alternatives (SEPY, SciTE, etc.) I started using Eclipse again. Its been installed on my system for quite a while now for experimenting with MTASC integration but haven't really used it for any actual Flash development until now. Gotta love it, what an incredible framework especially if you take the time to install some extensions.
With the announcement of Macromedia building its next generation Flex IDE code-named Zorn on Eclipse you really need to go check it out!