The implications of switching to Visual Basic .NET are that you will have to completely rewrite your applications written in earlier versions of VB. It is worth noting that Microsoft has included an upgrade tool. When you open VB6 applications in Visual Basic .NET, the Upgrade Wizard runs automatically. How well this will work on real-world applications is the real question. Run against a simple HelloWorld application written in VB6, the wizard produced a lot of extra code to support compatibility. (The HelloWorld upgrade and the original application are available for download from www.samspublishing.com.)
Besides providing upgrade assistance from VB6, Microsoft has already made minor compatibility concessions to Visual Basic .NET to support modest backward compatibility, but this in and of itself does not mitigate the need for completely rewriting VB6 applications. The benefit of rewriting is that you will be able to do more with less, and take full advantage of Visual Basic .NET. The implications of not rewriting may include code that is significantly more complex than it needs to be and difficult to maintain, and you may still have to rewrite major portions of upgraded code to cobble it together.
The need to rewrite existing applications may protract adoption of Visual Basic .NET more than a simple upgrade would. However, the benefits will be tangible to all customers and programmers alikeand ultimately, well worth the effort.