When Mint 12 becomes available will it be a simple matter of upgrading from Mint 11 to Mint 12.? I am well impressed with Mint 11 and don't want to bodge it up attempting to upgrade and messing up the whole system.
The recommended way of upgrading is to backup what you need and do a fresh install over your old install. You can keep a /home if you have it on a separate partition (recommended), then using the Mint Backup tool backup your installed software list and after you have installed the new version you run it to install the s/w again. I tend to also backup my entire /etc folder as I have a lot of tweaked files in there, fstab/exports/configs etc. If you have a "normal" install with one drive and no network shares the standard backup routine will work fine. If your /home isn't on a separate partition then I would recommend moving it to one first it makes upgrading MUCH easier.