Fully Open Source NTFS Support Under Linux
Well, you can bet your ass that Windows's native NTFS is much faster than the Linux one, because they wrote the FS, and they have years of time to optimize the working driver.
Sure, user-mode will be a performance issue, but I think the context-switch + work is only necessary, when the kernel decides to either read data (on a cache miss) or write out its file buffers to disk. So if you don't use NTFS as your native disk (not sure how that'll work with permissions and stuff), you should really by fine. Maybe there's an option somewhere to turn on big read-write chunks (so that the kernel will always read/write huge blocks from the user daemon, which would make context-switch time negligible).