you could say that several types of domain hacks evolved,
personally don't like ones that dismember single words into multiple parts with a dot
we've already witnessed del.icio.us, which was unique at the time,
but now if you do it, how will it look? like another copycat?
there is a reason why they eventually changed to delicious.com
its called user experience
Doesn't mean there aren't some cool ones with a single dot
another example is
Wall Street => Wall.St
Melrose Place => Melrose.Pl
....
...
what are some other ones?