This is exactly why me and my brother bought these. I have 'his' PogoPlug in my house and he has 'mine' at his. I have a two hard drives, one here and one there. And he has has the same set up.

What we did was back up all of our stuff directly from our computers and then swap hard drives last Thanksgiving. I use it for off site photography back up and add about 4 gigs (via drag and drop) per month to my off site back ups. I don't know what he is doing.

One thing to note -- there is only one account for both PogoPlugs. We each have an email address registered, but they must use the same password. Because of this, I see his drives and he sees mine. I was using multi-drive mode and disconnecting his after launch, but now I just use single-drive mode (all the drives appear as sub-folders) and ignore his drives. I trust him so it is not a big deal -- but there was, early on, on issue where he accidentally made a partial back-up to my photography drive.

About your actual questions. I think that if you activated the PPlug at your place and just moved it to your brother's all would be fine. The activated PPlugs are associated with an email/password account, not an IP address. Use the same account and you will get the 'cloud' effect of all one storage box.

I have tried ActiveSync a few times. But it did not do what I liked. I never ActiveSync-ed from my computer -- just from my local PP drive to my remote PP drive. The issue that I had was that after ActiveSync copied them they were re-time stamped at the time that they were copied. When I drag and drop to the remote drive, all of my pictures keep their original time stamp.

It was nicer because the local copy of 2-4 gigs of photos would be mere minutes. Then ActiveSync would do the 30-90 minute copy to the remote drive.

Another issue was that deleting them from the local ActiveSync drive and/or moving them out of the remote ActiveSync drive would break the ActiveSync. Maybe if I had turned it off first, then turned it back on after the delete/move it would have been fine. (I keep my pictures in very specific folder hierarchies.)

I don't know what you mean by 'initial setup'.

I got my PogoPlug before my brother and just set up an account.
Then my brother got his and set up an account -- with the same password.
Then we did a test and he added my email address to his account. Then poof! Our two PPlugs were interconnected as a 'single cloud service'.
(I recall that there was some sort of confirmation box that opened about confirming that I had rights to his PPlug. I think I just put in the password again and then they were linked. It was almost a year ago, so ... ?)

I also opened another account using a different email address and shared a folder on my local drive with it. My local drive is really for fun. This way I can access it without seeing either my critical backups or any of his drives. Kind of like an admin account and a user account.

Does active sync run locally on the pogoplug or does it require an active connection with a PC? In other words, if I start an active sync, then shut off my computer, does the pogoplug continue with the active sync job?