Yep, I work in Haidian.
It is a really big area, so it depends where you're going to be. Haidian is where pretty much all of the universities are, so there are a lot of students living here. There's an area called Wudaokou which is around Qinghua university and is very "young," with a lot of cafes, bars, foreign food places, people selling stuff on the street, etc. Haidian is pretty central and it is fairly easy to get to other districts like Dongcheng and Chaoyang where there's also stuff happening. Haidian is also home of Zhongguancun, which is Beijing's technology corridor, where you have Google headquarters, Microsoft, all sorts of computer/IT stuff going on.
I live between the West 3rd 4th ring roads in a fairly boring little corner of Haidian. I guess it is a decent place for us since I have 2 kids. We used to live near wudaokou and it had just a bit too much of a college town vibe, which made me feel old! The only complaint I have about the neighborhood is that transportation is not that convenient as there are no subway stops nearby and busses in Beijing are really slow. But that's just my neighborhood, Haidian is frickin huge.