Actually the default behaviour always was to press the third button, i.e. the scroll wheel to paste. Most probably the default setting doesn't include the "Emulate3Button" directive anymore, because everybody had a scroll-wheeled mouse for years nowadays :)
What can you do? Search for the "Emulate 3 buttons" option in your mouse control panel; alternatively edit /etc/X11/xorg.conf and add the line to the corresponding section like this :
Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5 6 7"
Option "Emulate3Buttons" "yes"
EndSection
<rant> Please notice that most current distros don't come with /etc/X11/xorg.conf anymore; the X server automatically sets up itself, with the very annoying consequence that when the default automatic setting doesn't fit your taste, it's a pure PITA to change.</rant>
1I hate the weird trend in recent releases to make things less transparent and harder to configure. How does putting X config in this weird four-levels-deep subdirectory with opaque grammar make things better? – CarlF – 2009-12-08T15:44:52.007
Eh, at least it has support for hotplugging now. (I heard they're going to get rid of
hal
soon though.) – user1686 – 2009-12-08T18:37:19.570