I just had to use it there today for a page that wouldnt print or allow me to copy text,
1) First time round: it repeatedly captured the taskbar (but a blackedout taskbar so ended up with repeated black stripes cutting across the image)
2) My taskbar hides (ausblenden), so i tried setting it to foreground/no hide & the screenshot worked okay.
Just tried it again, as in 1) above & it just siezed up.
[That was: Ctrl+Shft+PrtScr, then, Ctrl+Shft+Click; with Opera 9.01(edit), & WinXp]