Assuming a brand new, empty, WHS 2011 + DrivePool:
* before you share any folders in it, use Disk Management to change the DrivePool drive letter to something like Z: or P: or whatever. Windows has an annoying bug of sometimes bumping drive letters if you add a new drive later on, so pick one away from your existing drive letters if you can
* add at least one data drive to the pool (e.g. drive) - ignore any Windows error about Shadow Copies
* use the Dashboard to move your default WHS shared folders (Documents, Music, Videos, etc) into the pool
* optionally, add any additional shared folders that you want on the pool, so long as they're not called "Shares"
* personally I recommend leaving the Client Computer Backups folder out of the pool, but if it works for you, make sure duplication is turned on for that folder.
You can start at this point if you've already been using WHS 2011 + DrivePool for a while. Caution - where I say "use Explorer", I mean use it via Remote Desktop or logged directly into your WHS machine, NOT use it on your workstation (since we're using it to access the WHS drives directly, not their network shares).
* use the Dashboard to add all of your DE data drives (and any other drives you want) to the pool
* use Explorer's "Tools" menu, "Folder Options", temporarily enable "Show hidden files, folders, and drives"
(so that you can see the hidden Drive Extender and DrivePool folders on each drive)
* use Explorer to move (not copy) eachdrive:\DE\Shares to eachdrive:\PoolPart.guidstring\Shares
* I don't mean moving the individual subfolders under Shares, I mean the Shares folder itself!
* once you've moved the Shares folder out of each drive, you can safely delete the old WHSv1 DE folders
Once you've finished moving everything from DE to DP, use Explorer to view your drivepool drive:
* you should see your Shares folder
* bring up its context menu (usually right-click), go to Properties, Security tab, Advanced, Owner, Edit
* choose Administrators, tick Replace, then OK, OK, OK, OK.
* again bring up its context menu, go to Properties, Security tab, Advanced, this time Change Permissions
* remove all non-inherited Permissions, tick Include and tick Replace, then OK, Yes, OK, OK.
* if this doesn't go according to plan, investigate and/or seek advice
Now that any wayward DE permissions have been (hopefully) dealt with:
* use Explorer to rearrange your folders, files, etc, on the drivepool drive to your liking, e.g. you might want to move everything under \Shares\Videos into \ServerFolders\Videos - and you don't have to keep the Shares folder if it ends up empty - or you can just leave it all as it is if you were happy with how you had your old WHS folders set up
* you'll be warned if you attempt to move, rename or delete a shared folder - HEED THIS WARNING
* use the Dashboard to "Add a folder" (NOT "Add a folder to the Pool") so you can "Browse" to the folders you want to share with your network from the drivepool drive
* use the Dashboard to enable duplication on the shares that you want to have it
* if you don't want to wait for the nightly check, use the Dashboard to force a consistency check by DrivePool to find any remaining problems.
* if you want a folder duplicated but not shared, you can share it, enable duplication, then stop sharing it.
* DrivePool happily uses drives even if they don't have a drive letter; you can free the letters via Disk Management (in Explorer, right-click Computer, click Manage, click Disk Management in the tree under Storage, right-click the drive letter, click Change Drive Letter, click Remove)
* keep in mind while DrivePool can use drives without drive letters, Explorer can't - if you want it to see them you have to give them their own drive letter or mount them as a path under another drive that does have a letter
* don't remove or change DrivePool's drive letter while you're sharing folders in it, it will break those shares until you put the letter back
And that's it. Please let me know if you spot any errors or need further info.
EDIT 2012-04-20: added Otis's tips re enabling display of hidden folders and re removing drive letters.
EDIT 2012-05-24: noted if Client Computer Backups kept in the pool, recommend duplication is on for that folder.
EDIT 2013-01-08: added tslrulz's tips re Disk Management, shadow copies, empty folders.