Note that if a distro does have the trunctuation set up, steam will quickly surpass the 500mb limit and erase all of the logs that may be very pertinent to a user trying to track down issues on their system, as the normally very valuable ~/.xsession-errors log is filled with idle banter about a game running rather than holding the errors thrown by their system.
Nothing extracted yet.
For some reason ALL of steam's stdout output is being sent as stderr and being caught by the ~/.xsession-errors log. This log is for errors, not plain logs. Most linux distros have a system set up to trunctuate the log if it gets over 500mb.
Other (less popular) linux distros do not have this set up, and have thus exposed the issue. I am running #! 11, based on debian wheezy. While others may say this is an issue with my distro, it is absolutely not. The ~/.xsession errors log can grow over time, but it is usually very slow, on ther order of maybe 100kb a day, MAX, as it only logs stderr, thus only requiring attention once a year or so, and it's growing is a sign that something is wrong with your system. With steam sending it's full stdout log to the file, it grows to gargantuan sizes very quick. It filled up 109gb of space in less than 90 minutes (X3TC) with data that is irrelevant to error logs. The average growth while running games seems to be ~1gb every 2 minutes.
I can stop this behavior by launching steam with "steam > /dev/null 2>&1" which means sending all stdout logs to /dev/null and sending all stderr logs to stdout, thus deleting them. This is rather hackish as it hides all logs from the console, so if I am running steam from the terminal I cannot see if there are errors, and all of the real errors sent as stderr are deleted upon reception, thus limiting my ability to find and fix bugs when they happen.
edit
Yes, I have reinstalled/redownloaded steam, both the beta and the regular, both experience the same issue.