I was delving into ASP.NET MVC Preview 4 for a small project and I got hung up on form validation.  Currently ASP.NET MVC provides no way to validate form input against the model objects.  Form validation has to be written client side in JavaScript and server side in the action.  I would really like to be able to decorate the LINQ-to-SQL objects fields with validation information like Rails does.  I also hope they add some validator helpers to the the HTML helpers.

I see that someone else ran into this and went ahead and coded a solution for it the Forms Framework with Validation for ASP.NET MVC.  This is an interesting approach to the problem I am not sure how it would deal with forms that are using more than one model.  I want Microsoft to address this feature rather than cobbling basic functionality together from a lot of little side projects that may not see any further progress after their initial development.