I am a potential Fall 2010 or 2011.
These are several schools that have Fridays as visit days. For instance, some of the Booth's live days are on Fridays, making it easier to miss only one day of work.
Also, take advantage of the weekend to visit the city and see if you can see yourself being content in that area, not just for the two years during school, but eventually post MBA since you could end up in that general area.
I used this forum and the MBA books to form a list of questions before the visit, and then answered most of them from online information. Then the questions left over were more school visit specific, which is truly the reason why your visiting the schools.
If you can not miss Fridays, I suggest visiting on the weekends, and trying to email certain students working at the admissions office, to see if they can provide feedback, or if they could direct your emails to specific groups. In the end, you want insider information that you can use for your essays. Visiting the campus is good to get a good general feel, but information that distinguishes one school from the other is key when your writing essays on how you see that "X" school fit for your post MBA goals.
Each school is different, and finding out why "X" school fits for you is essential for your essays. Hope I didn't ramble too much.