How can I copy the content of a cell in the output pane where the latter is detached from the query window in pgAdmin III?
For reasons best known to the designers of PgAdmin3, it's apparently not possible to do this. 

The Cut/Copy and Paste options become greyed out when the window is floating. The logic behind this escapes me (wracks brain.... no, no good).

The only thing that I can think of is to use the green write arrow with the floppy and save your data to a file and dig out your data element that way - cumbersome I know. Or, you could just re-dock the window which does work.

If you'd like to file a feature request on the PgAdmin site, I'll gladly file a "me-too" if you provide the link back here.