I thought someone had already mentioned this issue, but a search on "paste" doesn't turn up the thread, so I'll mention it to be sure.
I ran a game using Roll20 in a Google+ Hangout. My browser is Firefox 12.0 and my operating system is Mac OS 10.6.8 I had the map zoomed to 50%.
I had trouble with the fact that when I copied a token and pasted it the copy appeared in unpredictable places. Sometimes it appeared perfectly superimposed on the original, so that it couldn't be seen. This was especially troublesome when I was having trouble with a lag of a second or more between typing command-v and the paste occurring. Sometimes the pasted token appeared on a part of the map that was outside the window because of zoom and scroll. Twice it appeared behind the toolbar where I couldn't select it. And pretty much the rest of the time I had small, dark tokens appearing at unexpected places on a visually busy background, and they were hard to find.
Ideally I would click somewhere, type command-v, and the token would appear at the point I clicked, but if that would be difficult, anywhere onscreen would be okay so long as it was always the same and not behind the toolbar.