I'm not even sure whether this is a feature request or a bug report. However, with the really great new windows 7 style 'group buttons' setting on, when a window in the group wants attention, the whole stack will flash orange; but there is no indicator (that I can see) which window in the group has a new message/etc. This is in contrast to window 7's own button stacking, where on mouseover one of the preview panes is flashing orange, to indicate which specific window is trying to get your attention.

For those of us used to working with 8-9 IM windows open at a time to juggle tech support requests (are there any other of us, or is it just me, I wonder?) it's a noticable issue, whether it's a bug or just a missing feature.