I am using Instant VB from Tangible Software Solutions to convert all of my code samples from C# to VB in my upcoming book Data Services with Silverlight 2. It is allowing me to write all of my samples in C# and then use this tool to convert them to VB. So far I have had very few problems and most that I have had have actually been fixed in service releases recently. This is great since all of my samples for the book both in print and electronically will be able to be in both VB and C#.
The only issue I have seen lately is in converting service references to WCF and ASMX proxy classes. For example, the proxy class definition that gets added to a Silverlight 2 client is not converted properly when I use Instant VB. I am going to pass this along to Dave at Tangible to see if they are aware of it and have a fix. He has been great about getting fixes in and getting back to me.
Instant VB and Instant C# are great tools. They allow you to convert a snippet of code, a file, or an entire folder structure of code. And the speed is incredible. It rips right through the code in seconds most of the time. I ran it through a medium/larger solution with about 500 files and it converted it in about a minute. Not bad at all! There are some free tools (with less features and much slower generally) but so far this tool has really blown me away.