Top down - any problems?

The Spider manual says that the hood should not be left down for any protracted period to avoid damage. So I've been putting mine up every time I put it to bed at night. But the dealer I bought it from had the top permanently down whilst it was in his showroom - and I guess most other Spiders for sale would be displayed the same way.

Am I being too careful - or has anyone else actually had problems with leaving the hood down for too long? How long is "protracted"??