I think that my views echo those already posted. I've owned an older convertible from another manufacturer that leaked horribly. I know people who have convertibles made by Volvo and others by Saab, and they sometimes leak too.
I think that it is important to understand what you are getting with a convertible that makes it worth the small chance that you get some leaks. With almost ALL convertibles, you are getting a great looking car that opens to the sun and air. All the benefits of a motorcycle, but with all the safety of a steel re-inforced cage and fancy sound system.
If you purchase the car-- I strongly feel that you'd be happy if you did-- I suggest that you get one of the small bottles of VW brand roof-seal-lubricant. If you would like details about the lubricant, or would like to see pictures explaining how to apply it, please check out this link: http://forums.vwvortex.com/zerothread?id=3087297
With that lube-process done to my car, it has not leaked, squeaked, or caused any grief at all. I've even tried to test the seals with a pressure washer, with some amazing results: http://forums.vwvortex.com/zerothread?id=3118009
(you'll need to scroll down to find my post in that thread)
Anytime there are moving parts, there is always a chance of problems. I'm enjoying the car enough to make it worth the risk-- having the hardtop fold away is fantastic, but actually driving with the top missing is... well, you just have to do it...
My vote: get the car, I think you'll be happy with it.