Since 10.7 you can use Command-Shift-X to toggle viewing vs controlling in Screen Sharing.

So you can switch from the remote machine to the local machine from the keyboard depending on which one you want to use Command-Tab.

I can't make CMD-SHFT-X work in ARD, nor do I see an option for this in Services. Is there something I'm missing?

The shortcut is actually Cmd-Opt-X.

ARD 3.6.1 and that doesn't work for me either.

I for one, like the fact that command-tab and other functions go to the remote machine. It's as if you're sitting at it, which is nice. When I use other screen sharing apps, I get annoyed when command-tab and other commands only work on my local machine, especially when trying to change "spaces", because many times there's no other easily accessible way to do it on the remote machine. I think some things that would make remote machine work easier would be:

1. Something to make hot corners easier to activate when not in full screen mode.
2. Drag and drop to copy files to and from the local/remote system.
3. Warning dialogs when your system decides to quietly turn off back-to-my-mac (happens to me on occasion)
4. Back-to-my-mac shortcut icons for specific machines I can put in my dock (actually, I think I may have just answered this one myself - You can save a .vncloc file from the file menu of the Screen Sharing app)
5. A keyboard button (with an LED) to enable the screen sharing server and/or back-to-my-mac for when your monitor dies so you don't have to ssh in and muck around with defaults write commands
6. More intuitive copy clipboard icons (it doesn't make sense to me)
7. A listing of back-to-my-mac enabled computers to choose from when launching the screen-sharing app (instead of just a box to enter a host URL)
8. The ability to enable at least a very lo-fi audio connection so you can hear beeps from the remote system or at the very least an audio level indicator in the toolbar or some sort of local tone indicating the remote machine is making a sound
9. When a back-to-my-mac machine is offline, show it greyed out in the side-bar with a warning icon you can click to get the status instead of removing it completely without a way of finding out why it's not online
10. Some sort of indicator on the remote machine that tells users physically at the machine that a remote user is logged in.
11. The ability to screen-share using a different user account in the background instead of the currently logged-in user
12. An iPhone app for screen sharing via back-to-my-mac (like LogMeIn)!!!
13. The ability to temporarily indicate a second Apple-ID in the screen-sharing app in order to share with a remote computer running under a different Apple account

OK people, let's get cracking on these hints...!

Dear robleach,
These are already true from your list:

2. Drag and drop to copy files to and from the local/remote system.
Works great in 10.8. Both directions.

7. A listing of back-to-my-mac enabled computers to choose from when launching the screen-sharing app (instead of just a box to enter a host URL).
I love "ScreenSharingMenulet". An oldie, but still works fine under 10.8. It lists all recently connected machines and lets you make a list of remote ones in a drop-down menu.

11. The ability to screen-share using a different user account in the background instead of the currently logged-in user.
The OS 10.8 Screen Sharing client already asks which account you want to log into, and goes into the background if it's not the current physical user. This step is skipped if you set a login username and password in Keychain, so check there if you don't see these options.

12. An iPhone app for screen sharing via back-to-my-mac (like LogMeIn)!!!
Any iDevice VNC app like "Mocha VNC" or "iTeleport" connects fine to Mac Screen Sharing servers. I use it all the time from iPhone and iPad.

If you're requests were specific to "Back-to-my-Mac" rather than just Screen Sharing, then maybe you need to run Dynamic DNS instead. The above recommendations find any of my servers regardless of dynamic IP thanks to DynDNS.