My observations on vanilla 3.1.1

[slinberg]

Forgot to mention: just ASCII.

According to MenuMeters, it pegs one of my cores to 100%; the others don't do much. And it's s--l--o--w. This is an 8-core 2.66ghz Mac Pro with 10.5.8 and 6 gigs of RAM.

[Pete Mack]

OK, I can't reproduce this, with or without graphics mode.
* Do you have ESP, and is there a monster in ESP range?
* What version are you playing?

Are you able to compile with gprof (-pg)? If so, try saving your character at dl 1, then opening it with a -pg -g compile, then resting 9999 turns, then exiting normally (and quickly.) Post gmon.out to the angband newsgroup.
Also post exactly what version (including svn revision, if you are using svn) you are using.

If you are able to analyze gprof yourself, that's even better! If you know a little programming, it's not very hard:

http://www.cs.utah.edu/dept/old/texinfo/as/gprof.html#SEC2