The Arduino IDE editor's lack of support for X11's select-paste mechanism has always annoyed me. Well, I finally got around to adding it. Especially for helping people with their Arduino troubles (which I do every day), it's so very nice to finally be able to quickly select-paste between Arduino and forum messages, email, terminal windows, etc.
This is a Unix/X11 feature. Mac & Windows do not have anything similar. But on Linux it's so very fast and convenient. This tiny little feature really makes me happy. :-)
Update: it's been accepted and will become part of Arduino 1.0.5. Anyone using 1.0.4 who wants this feature now can install Teensyduino 1.0.4 release candidate #1 to get this feature without having to recompile the entire Arduino IDE.