I've used my Boxster in the Washington DC area as a daily driver for the past 3 years. No problems at all with the soft top. It's an 05 so plastic window is not an issue.
Ahhh! I want a hard top. After the extensive suspension work coming up next week, hard top has to wait. I always liked the Zeintop but, could never get a quote I was comfortable with purchasing one. Cool concept, just came at such a high price.
Mine is currently off the car, though I think that after I get a few more open-top miles under my belt, I will put the top on and just leave it there year-round. I like the noise reduction and style that the hard top brings.