I usually work with an additional monitor plugged into my Powerbook at home, but not at work.
If I accidentally leave anything open on the external monitor before disconnecting everything, on restoring the affected application the window is pulled onto screen. That is to say, if at any time the desktop area is reduced, windows readjust their position so not to be lost.
TextMate doesn't seem to be doing this.
I connected up my external monitor this evening to find a window that had been 'lost' all day!
drew.