That's one of the weirdest things I've seen. They were working fine
ever since I found them earlier today, but I get the 502 Bad Gateway
now, too.

Luckily I saved the two pages as PDFs because they are useful; they're
available here:

<thadlabs.com/FILES/Ubuntu_8.04_Guide.pdf>
<thadlabs.com/FILES/Ubuntu_8.10_Guide.pdf>

A Google search on "502 bad gateway" reveals it's a network error
at the server end, often caused by being overloaded; one report here:

<http://www.checkupdown.com/status/E502.html>

For what it's worth, "ubuntiguide.org" is in Kuala Lumpur which is
in Malaysia.

I just checked the internet traffic report and it appears Asia is
falling off the map. Maybe an earthquake?