Notepad++ is great for the price, and ends up on most of the customer systems I touch, but has a couple of annoying quirks, and is missing some functionality that you can get from the paid programs. The quirks that really annoy me:
1) The find function does not have an option to automatically dismiss the find dialog on the first match, so that you can just use F3 for further matches.
2) If you have multiple files open, and file change notfication set, when you agree to load a changed file, it makes that the active file, and starts a text select with the anchor at some random spot on the page. This is really bad if one of the files that you have open is being changed occasionally by another program (like a log file).
3) Default syntax highlighting changes not just color, but font, (to a less readable one) for comments in Perl and HTML.

Some missing features (compared to my fav, Ultraedit):
1) Limited sorting, no duplicate removal, no numeric, can't define multiple key columns.
2) no compare
3) no column editing mode
4) help is only available online, not much use on a plane.
5) doesn't automatically select hex edit mode for binary files.
6) No menu functions to trim all trailing spaces or convert all leading spaces to tabs. Could probably be done with a macro, but that is a hassle for a simple function.
7) No built in save to/open from FTP.