I think Visual Basic 6.0 applications will live for a long time, like COBOL applications, and for similar reasons. Parts of my company's products are still VB6, and they won't be changed until there's a good reason. We're hoping Microsoft won't be able to drop VB6 support for a good while because too many of their enterprise customers have VB6 apps. They've already been forced to extend the support period beyond their original plans. We're hoping Raymond Chen wins over MSDN magazine - obscure joke that will only make sense if you remember Joel's post about Microsoft's dilemmas with backward compatibility versus design purity.
If you're considering upgrading or rewriting, IMHO this question and this question have some informative answers. You can mix new .NET components with existing Visual Basic 6.0 using Interop, if there are .NET features you want or even if you just want to learn .NET.
The Visual Basic 6.0 newsgroups are still pretty active so there's obviously a lot of old fogeys like me still developing in Visual Basic 6.0 :)
Duffymo, Bruceatk - the Visual Basic 6.0 IDE can be made to work on Vista with a bit of effort.