Summary regarding observed .xsession-errors in Knoppix 6.2.1, Flash/usb version:

By far, the greatest number of .xsession errors were due to 'XID collision warning's
due to Flash-content. The amount of errors logged per unit time at varied greatly
with the site. Results for a number of sites are summarized in 'Flash-content errors'.
Adobe, Hulu and Newegg sites showed the highest rates of these errors.

A smaller, but more persistent set of six error types were also consistently noted.
These are summarized in 'Non-Flash-content errors'. The first two of these types seem
both to be related to PolicyKit problems associated with the Desktop Session Setting gui.
The third and fourth of these types of errors seem both to be related to Compiz
and/or another program not finding Clearlooks and Ubuntu Human theme material where it
expects to find it. The Sixth of these types of errors is due to an unset gnome
interface setting.

In response to these observations we have done the following.
1. Changed our /etc/X11/Xsession script to keep only the current .xsession-errors,
rather than concatenate each new session with all the previous;
2. Added SQLite Manager to IceWeasel and instituted an occasional compaction
of the urlclassifier3 cache;
3. Set /desktop/gnome/interface/accessibility to false (unchecked the box);
4. Reported the notes concerning Non-Flash-content error types one thru' four
to Klaus Knopper; and
5. Reported the notes concerning Non-Flash-content error types three & four
also to the Compiz forum.

The 'XID collision warning' problem has been reported everywhere for most every distro.
It seems to lie somewhere between Adobe and gtk as a responsibility to fix. In my
case, I see no performance penalty or crashes to worry about, and I've cut back on
the overhead to record all these otherwise meaningless (to me) .xsession-error reports.