Colin,
Guess I'll throw in my two cents worth: I have the Domino, a cheap biscuit cutter, and the Kreg pocket hole system. I deal with mostly plywood panels (building euro style cabinets) and frankly the Kreg gets used daily, the Domino occaisionally, and the biscuit cutter (since aquiring the Domino) has not been used.
The Domino is quick when you need a tennon, For the boxes (cabinet cases) I'm putting Kreg screws in where they won't be visible (under the deck, on top of the stretchers), even in the sides of cabs which will join other cabinets. Not through preference, but I do this for a living, the faster I get something finished, the more money I make, the Kreg is faster.
On the doors (5 piece) the Domino is king. Pocket holes are ugly and a pain to fill even with the plugs from kreg and a Fein to cut them flush. The domino makes a strong, invisible joint with no metal (in case I have to cut a door apart or "trim" it a little).
If you buy one (domino that is) first check the setup, seems like many people have got one (like I did) where Festool didn't set the sight gauge or the internal stops (Note to Festool employees, It's pretty damn annoying to find that the company (who could have set it up in seconds) leave it to the customer to set it up accurately (which takes a while)).
(nested parenthesis, guess what I used to do for a living) - I digress
Then Clamp the pieces, I often think the domino should have been a bench tool, that little router bit throws itself around a bit while chewing it's way into your project, given half a chance it will move itself just enough to ruin what should have been a nice flush joint. (Not a critism of the domino, just some hard earned experience)
Steve
Mod:
On second read through, I shouldn't have said it "ruins" the joint since the Domino makes it so easy to fix it (glue a domino into the hole that went wrong, cut it off flush and re-cut the hole).