Yah, sorry about that. With the anticipated inrush of new users, I've been trying to make the process as easy as possible for them.
My personal position on when to make the switch is to wait no longer than December, during the holidays would probably be the best time. I have no idea what Microsoft has planned in January. I suspect they will update the files for WMC to remove the option for their guide, but I don't know if they are going to do anything with everyone's recording requests. In December, everyone will still be able to convert their current requests (Rovi) to new requests for SD/Gracenote, but there are no guarantees to be able to do that in January.
The portable version is basically all the files without the installation package. It gives the user the ability not to "install" anything. You could also put it on a thumbstick and manually run it from there on any machine (though without a scheduled task to do it automatically).