Long-time xfce terminal user here. Just recently I noticed that having a terminal open causes high CPU usage especially in X. Htop shows terminal taking something like 13% of CPU time and X is taking a whopping 50%. If terminal has no text in it (ie. before any commands etc.) the usage is a bit lower, but still high. These percentages are for one core on a quad-core 2.8 GHz system.

I'm a Gentoo user with these dependency versions:
 * dependency graph for x11-terms/terminal-0.4.5
 `--  x11-terms/terminal-0.4.5  ~amd64 
  `--  dev-libs/glib-2.24.1  (>=dev-libs/glib-2.16) ~amd64 
  `--  x11-libs/gtk+-2.20.1-r1  (>=x11-libs/gtk+-2.14) ~amd64 
  `--  x11-libs/vte-0.24.1-r1  (>=x11-libs/vte-0.17.1) ~amd64 
  `--  xfce-base/exo-0.3.107  (>=xfce-base/exo-0.3.4) ~amd64 
  `--  dev-libs/dbus-glib-0.86  (>=dev-libs/dbus-glib-0.31) ~amd64 
  `--  dev-libs/libxslt-1.1.26  (dev-libs/libxslt) ~amd64

I'm running kernel 2.6.34 and Compiz 0.8.6. Terminal transparency has no effect to the CPU usage. Xterm and gnome-terminal don't have the problem.

I tried to downgrade vte library (I believe that's the dependency most recently updated) but it didn't compile anymore so I couldn't check yet if that was the reason. I'll try looking at it.