Looks like a mature selection of the straight species Acer palmatum. This can get to be a pretty good sized tree over time and is also rather variable in leaf size and formation, but the dissected/heavily lobed leaves certainly indicate a palmatum.

A few people on the Trees forum identified it as a large Japanese Maple.

What do you think?

Here is the link:
http://forums2.gardenweb.com/forums/load/trees/msg0722381113089.html?21

Acer palmatum = Japanese Maple.

As GardenGal said, this looks like a generic green Japanese Maple. There are over 500 kinds of Japanese Maples, which makes it difficult to make an exact determination from looking at a few photos. Its a beautiful tree, however, and that's what matters the most!

Regards,

K4