Bigtex,
I'm from Chicago and have run it a couple of times. Was hurt last year but ran it in 2001.
The course is almost completely flat. The only hills are bridges and exit ramps. Since it's a loop, whatever wind there is will get you for part of the race. Sometimes in mid-October, you can get a 40 or 50 degree day with no wind, and if so, the course is lightning fast. Last year it was colder, around 30 I think, with a pretty stiff wind out of the north (in your face the first 7 or 8 and last 3 or 4). It can also be pretty warm that time of year, but if you're coming from Texas my guess is that's unlikely to be a problem for you.
Crowds are great in the first half, but the second half is pretty desolate other than in a couple of neighborhoods.
It is a huge event -- I think they raised their limit to 40,000 this year. Extremely well organized. Some people complain that the crowd of runners is so thick that it's hard to run for several miles, but if you get a seeded number (3:10 for men), I haven't had any problems with that. The nice thing is that you're likely to have someone near you the whole way. At Motorola Sunday I ran from 3 miles on virtually alone -- caught a few people from 10k on but never found anyone to run with for any length of time.
Good luck at Boston.