I also can't complain that a huge bitmap was sent: it arrived as a 139Kb message.
The gripe? It was a full screen capture. There was no thought of resizing the window and using Alt-PrintScreen (grab active window), or even grabbing the one window in its maximised state. Anything more than "PrintScreen, Paste" is too difficult.
In fairness, I expect many people don't even know about Alt-PrintScreen. So, there are two problems. Firstly, operating systems don't seem to provide readily accesible tools for capturing part of a screen - it's either full screen or active window. Secondly, even if the capability was there, users would either not be aware of it, or not bother using it.
On a related note, I want to find a better screen capture utility for MacOS X. On Windows, I'm using the freeware MWSnap, which is flexible and allows cursor-controlled precision. MacOS has Grab, but it's not quite what I want. Similar situation with KDE.