Really it comes down to what vinyl-junkie mentiond. OOP
If you're comming from a classic asp/vb6 environment, then sure it's going to be a different beast to take on to learn .NET but it's a step in the right direction if you're looking to become an object oriented programmer. It's not just going to be learning a new language, it's going to help you learn about OOP in general.
If you're on a goose about how you despise microsoft because of IE then well, lets take a look at php, php is taking the right direction towards OOP, but their not microsoft so are you saying you're willing to take that on? I don't know about you but I don't just use one language, and knowing multiple languages is a huge plus, and even though the syntax is different, the conceptual idea of OOP is the same regardless.
The list could go on and on about the major differences from classic asp/vb6 to .NET. But if you were to ask me, the pros would outweigh the cons tremendously.
It looks like this started out as a question about C#, to a discussion about upgrading to .net then to IE. So I really don't know where to start or begin when theres so much to cover. I at least hope the original posters question was answered.