I spent a few enjoyable days on the south coast of England in Cornwall at Sennen recently (very nice!) and ended up reading my copy of
Mac OS X Hacks. Its a great book and well worth buying if you've moved to OS X. I learnt quite a bit, especially as I'm a newbie Apple user this year.
The tip of the day which I learnt from the book is the open command. It works from the command line in a tsch or bash shell. Just type open and a file name pattern and it'll open the file using the OS X GUI tool associated with the file type.
Quite handy if you just wanna popup a Folder of a directory you're in or a graphical editor tool of some HTML or whatnot.