Just my opinion, but we moved to .Net for our product development around 10 months ago, and I think that it has resulted only in good things, well nearly only good things. Although we use c# not VB.Net, I think the issues encountered could be similar. Just before delving into it, we develop web applications (e.g. OLAP analytical tool) and usually use WinForms for internal testbeds only (ie no products in field).
For us the biggest downside of changing over was our people not knowing enough (from our training or their personal study) about what the .Net framework offers the developer. Conversely, these improvements provided by the framework are what is making me rave to everyone I know about the .Net framework, and ASP.Net in particular.
If you're looking for productivity gains, look at how you are:
Classic asp --> ASP.Net
- Debugging (classic) asp --> Tracing ability within ASP.net rocks, plus whilst in System.Diagnostics, do some writing to the event log to help your production debugging
- Writing pages to handle differing browser types --> ASP.net server controls
- Multilingual issues --> use resource files, change thread context and presto
- using tables to place *everything* --> try out the Placeholders and Panels
- Data entry validation --> try the validation controls
I could go on and on. Basically our guys were doing heaps of client side script, tables and basic hoop jumping to do their *magic* , that (most) of this is available from the server side using a strongly typed language (of choice, go for VB.net or c# , or cobol.net :-) ) is in my opinion better than sliced bread.
Yes, our guys had to learn c# (all previously VB6 developers - com+ & asp focus), and yes, the initial curve was steep and approx 3-5 mths (depends on dev level/experience) but the benefits are and can be huge.
Frequently, I am caught telling people I wished we had ASP.Net (including the webservices) 2 years ago.
Enough raving, we have found that our productivity has increased and the standard of code/product produced is much higher.
Yep, we're a MSft shop too, does that make me biased? Keep in mind you're reading this on SQLSERVERCentral.com, not Oracle or Sun :-)