Shutter is nice, but it's not an elementary-styled app, and it's a bit hefty at times.
Is there an alternative for quick screen-shots?
The default one is gnome-screenshot and as far as I can tell it respects the HIG guidelines (see window decorations).
Looking through 3rd-party solutions specifically developed for elementary OS, there's a similar tool which makes use of a dark theme.
There is also a request to pull it in as the new default screenshot tool in the next release of elementary OS.