One reason people like TextMate so much is they can browse to any file (shell script, properties file, xml file, yml file, etc) and right click and hit "Send to TextMate" and they can quickly look at/edit that file.
Or from command line type "mate blah.xml" and the file pops up.
In IntelliJ/RubyMine you have to create a project, add in the file, etc. Terrible for a quick look at a file. Terrible for a one/two time usage.
I know the product isn't designed as a general purpose text editor, but the IDEA editor is phenomenal. Seems a shame not to leverage it for general purpose.