It runs fine technically, and the interface isn't too bad, it just doesn't smoothly popup from the taskbar. When you click the icon it just plops itself on the desktop, there is no smooth action like other applications that use the windows animations.
Other applications have an animation when minimize and maximizing from taskbar, and when you first open an application it does like a fade in effect. I would have thought MC/MJ would have had it from the Vista Aero, but I haven't used Vista since its release. 7 however is very nice. Wouldn't mind seeing a glass theme introduced to match 7 but that might be asking too much.
Its a small complaint but I think a valid one.
Also, I think a lot more people will be going x64 with Windows 7, I know this is a little off topic but is there any advantage in making an x64 version of MC/MJ. I noticed you have the memory playback... being able to use more than 3.25gb ram will be cool. But then I guess the ram playback is a sort of buffer... My current computer is running 4gb ram, but most people I work with are running more than that already.