A lot of sub-2:35ish goals ok here, and that's where I want to be! Trying to go out slow (keep it above 5:50 the first few miles) and pick it up as I go. The heat doesn't really scare me, but I predict a lot of "dead horses" out there in the final miles (could be one of them!).
I've run this a couple times and trained extensively on the course, so here are some tips for first timers:
--it's flat and fast: the only hills you will probably notice are just before the half (I mean on Franklin, not Adams...but any bridge will give you at least a slight uphill) and...a not-so-nice steep trek up Roosevelt about .25 miles from the finish
--crowd support is generally fantastic, with the sections from miles 8-9 (through Boystown on Broadway) and 21-22 (look for the dragon in Chinatown) being definite highlights...on the flip side, miles 14-16, which wrap around the United Center is where the crowd can get a little thin
--a lot of the course is oriented so that you get a clear view of the Sears Tower...if you blow up your race or aren't running for a specific time, make sure you look toward the beautiful Chicago skyline (you'll have an idea of how much further you have to go that way)
--(probably goes without saying, but)...this is a world class event and you will be running the same race as some of the best in the world...so make sure you take it all in no matter where (or whether) you finish.
--one final note: the last strech down Michigan Ave can seem endless if you are struggling...look to the street numbers to grind out those last 2.5 miles if necessary (the ballpark is at 35th, you will head east until Michigan and then go north until what would be 12th street...the Sears Tower sits on Adams 8 blocks up and 6 short blocks over if you need a more visible landmark). Also, and I'm repeating myself here, but I cannot emphasize how much I personally dislike having a major hill so close to the finish...but if you've never seen it, you might want to walk up Roosevelt (1 block south of Balbo) just to get a feel for what is the only major uphill you'll have to tackle (on the plus side...make it up that hill and it' about 250m to the finish!)
Good luck..and (if it's hot, don't be afraid to slow down)!