Currently, the Pogoplug PRO does not support Time Machine integration - it's a feature that is consistently asked for on the forums here, and the folks at Cloud Engines are aware of the numerous requests here.

Of interest to you might be the upcoming Buffalo CloudStor (announced at CES 2011), which does support TIme Machine, although I imagine that is separate from the Pogoplug integration in the device. The CloudStor also has storage built in.

http://www.pogoplugged.com/blog/entry/15390/Buffalo-Announces-CloudStor-First...

Of course, if a future version of Pogoplug (or the existing software) is updated to support Time Machine, we'll definitely be posting about it here.

Peter Redmer
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There are ways to get a pogoplug to act as a time machine but it takes knowledge of linux. One is using optware: http://www.nslu2-linux.org/wiki/HowTo/TimeMachineBackups
And another is using plugapps : http://www.plugapps.com/index.php5?title=Application:Time_Machine
Like Peter said, these two options are not supported by cloud engines. They both require installing AFP and avahi so the shares will show up in Finder, almost as easy as a time capsule but not throug airport. I have used them reliably with both 10.5 and 10.6. With optware, I backed up 80
GB and Plugapps 140 GB. I have them running continuously for some about a week. I have tested restore using both quite successfully, about the same as a USB drive connected directly. But again, you have to know Linux and If your not comfortable with it would advise agains it.

As Peter has also mentioned, The Cloudstor already does all this for you.

As an attempt at something quick and dirty, you could type in "defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1" using Terminal. It is from the web page http://discussions.apple.com/thread.jspa?messageID=5918065 This might allow a mounted share to show up in the Time Machine setup. I am assuming that you know how to set up a share in Time Machine.

By the way, great tip arfarf!
So jaboo, let me get this straight. You have an actual time capsule which you are using for time machine backup. Now, you attached your pogo plug (model?) to the network and you lost your connection to the time capsule? (sounds a little off topic)