We regularly monitor the forums at http://social.msdn.microsoft.com/Forums/en-US/vswpfdesigner/threads, and that is the best place to start a conversation with the team.
Additionally, you can leave comments on blog posts on this site.
We are happy to take bug reports on the WPF and Silverlight Designer forum, but (in case you were not aware of it) if you have found a bug in the designer (or anything else in Visual Studio) the best way to report it is via the product feedback center (aka "Microsoft Connect"), here: https://connect.microsoft.com/feedback/Search.aspx?SiteID=210
This allows you to track the progress of the issue, which is harder to do if we open a bug report for you in our internal systems. Also, customer reported issues get higher priority, so it's more likely to be fixed.
Sometimes bugs are hard or impossible for us to reproduce, which makes it very hard for us to address them. If you can let us know what the exact steps for creating the problem from scratch are then that makes it easier for us to track down and fix the bug.
You can also attach a solution or project that reproduces the problem. If at all possible, please narrow down the code and the solution to the simplest possible form that reproduces the problem. This should also avoid you needing to send us any of your company's intellectual property (we don't want any of that please).
Please also let us know what behavior you expected. Any other relevant information about the environment might be useful, such as whether you've tried it on more than one computer, whether it's always happened or just started and so on.
If you have a crashing issue or a performance bug, there is a helpful tool for capturing a crash dump or performance trace available here . Capturing a dump for a crash or a trace for a performance issue will usually make your bug report easier to act upon.
Suggestions can also be reported via the same web pages - we appreciate those too, big or small. Thanks in advance for all your feedback.
http://social.msdn.microsoft.com/forums/en-US/wpf/threads/ is a great place to start.
http://forums.silverlight.net/ is a great place to start.
No, this is not a supported scenario, and is not permitted for Visual Studio 2008 or 2010.