II am now running Ubuntu 10.10 – Maverick Meercat – under WUBI. It is all working. There is no discernible slow down. It seems to me, that if you want to install Linux on a Laptop, the WUBI is a much better way to go than creating a special partition for it. If you make a separate partition and install Linux on it, every time you restart the machine, it drops you down into Linux instead of Windows. You can change this, but it is all extra work with a good chance of messing up your machine. I know because I have been there! An expert in the Linux world is described as being one who has made every conceivable mistake.
Ubuntu with WUBI