I have had highly minimal VB6 experience, but as for whether to learn it or not...
Visual Basic 6 is officially a dead standard, and indeed, a lot of companies have migrated to VB.NET now. New development is done in VB.NET and most jobs ask for developers with .NET experience.
Nevertheless, there is still a decent chunk (a couple of million, I think) who use VB6 substantially. Not to mention, there are a ton of legacy applications that must be maintained.
I say learn VB6 to a level decent enough for code maintenance, but if you want to pursue serious endeavours, learn VB.NET. It is the modern standard.
(personally, I'm not a fan of any .NET languages, but there is a large market for them)