Microsoft recently posted about the new VS 2010 SharePoint Power Tools project. Right now the contents are pretty slim, but the two things that are in there are freaking awesome. Both relate to the new Sandbox Solutions.
The two things the VS 2010 SharePoint Power Tools give you are the ability to include visual Web Parts in your sandbox solutions (which you can't do without these tools) and also some compile time checking when building your sandbox solutions. This second one is the coolest one to me.
When you are building sandbox solutions, you are compiling against the fully trusted & full SharePoint API. However when you are running on the server, your code is running against the subset of the full API using the special SharePoint sandboxed proxy API. This blocks you from doing calls to SPSecurity and the like. While this doesn't seem like a big deal when writing new components, it can be when you are copying code in or grabbing something from CodePlex. When you build everything looks good, but at runtime you hit issues.
Before these tools in order to verify you aren't doing anything illegal and to get compile time issues, you had to manually remove the Microsoft.SharePoint.dll reference from your project and point to the subset API assembly, compile, fix and then set the reference back. The power tools now do this for you! Nice work!
PS - both of these were in the CKS:DEV project, but I think they will be more widely used in a Power Tool set.