Personally, I dislike abbreviations in code.

Whenever I see something like regno, mgr, dept in code I'm dealing with and stuff like that I pause for a second and consider renaming it.
If that's a code that I'm going to be in charge of in the future, I rename it on the spot. However, if I'm only helping out a fellow developer I have to consider their own likes and dislikes - because it's not my code to change.

So, do you Abb. or never Abbreviate?