I code primarily under Windows, and I still use notepad for my "multi-line one-liner" programs. For anything more complicated, however, I use one of Activestate's editors: Komodo, a Mozilla-based editor of many languages, or Visual Perl, a plug-in to Visual Studio .NET. The latter isn't an option for many due to the price barrier, but for me it has the power that I like from something like Emacs with enough of a GUI that I can get all the information I want quickly and without losing track of my code. The integrated visual debugging that saves me a billion "print" statements along with quick access to the perldocs that I want allows me to avoid spending time opening a billion windows just to work on one program. I know that there are a lot of people that hate MS programs and Visual Studio, but it's perfect for a lazy programmer like me ;).
In general, I insist on using something that has good smart-indenting code. My error rate is greatly reduced that way. It seems like the only time smart-indents frustate me is when I'm sure they're making a stupid indent, only to figure out when I try to run the program that I really did forget to close a string, brace, paren, etc.