I'm a Madison, WI native. Just moved away to do something different for awhile.
It's pretty small as far as a city goes-- one of those places you could thoroughly map out in a few months. Nightlife and music is decent, but there's a definite lack of people in the 23-28 age range. Seemingly everyone's graduated and moved to a bigger city. So you're left with 1) younger college kids (scads of 'em) and 2) a more older, settling-down crowd. Live there long enough and you'll feel like you know everyone.
Downtown is small and integrated with one end of the UW campus. State St, the "main drag" is undergoing a long trend of replacing culture and color with chain stores and a giant "performing arts center." The state capitol is beautiful, but many condos are snatching up the views and adjacent neighborhoods. Really the best things about Madison are the lakes-- canoe, sail, fish, swim, all that. Ice fishing in winter. But it's also a curse, as it compresses and restricts the growth of downtown areas to a narrow isthmus.
It's a very pro-bike town. Lotta student commuters and year-round badasses (though people still think you're nuts for riding in snow). We've got a glut of bike shops (Yellow Jersey, Revolution Cycles being regared as the best) and hey, it's the home of Jonny Cycles and the annual Lord Of The Chainrings alleycat. There's also the Freewheel bike coop, but it's a couple miles south of downtown-- always kinda distant from where I lived.
Rent, expectedly, gets more expensive as you near campus. Williamson St. is a little pocket of countercultural-ish people, but even that area has seen a lot of rent inflation and, sadly, condo development. Yuppies. The near east side of town would probably your best bet. Expect $500+ for one bedroom apts, something like $800 for two bedrooms.
Didn't mean to write so much about it, but I'm a wee bit homesick...