Did you know that the Zagat guide recommends 26 (get it?) restaurants along the route? Not sure I agree with the list, but it's a good idea nonetheless. As you know, I generally watch the start on TV (Race coverage starts at 9am on NBC) then run out to catch the front runners. I've done it in Brooklyn and Manhattan, and twice I went to both boroughs.
I suggest finding the least populated spot to watch - that benefits both you and the runners. Those dead zones are killer for them, and great for spectators. Mile 20ish, Bronx, is typically the opposite of, say, Mile 16, Manhattan, where this year Food Emporium will be giving out snacky food and drinks, and there will be a DJ (that's 59th and First Avenue). If you really want to see how fast the fast people are, start on First Avenue then run over to Fifth and see them twice. They might beat you.
Watch the NYC Marathon, In A Bar
This year there are about 100 bands playing along the course, and Coors Light is doing some parties called "Race To Refreshment" since the beer is really just a can of water:
Becky's Pub, 1156 First Avenue, 12:00-1:30pm
The Wharf, 587 Third Avenue, 1:00-2:30pm
Bar-Coastal, 1495 First Avenue, 1:30-3pm
Baker Street, 1152 First Avenue, 3:00-4:30pm
East End Bar and Grill, 1164 First Avenue, 4:30-6pm