Just letting everyone know that the Optware set of packages that were originally ported for the Linksys NSLU2, and have been ported to over 20 other embedded devices since, seem to work perfectly well on the Palm Pre.
See http://ipkg.nslu2-linux.org/feeds/optware/cs08q1armel/cross/stable/ for the list of packages. People have already tested ssh servers, web servers, ftp servers, network analysers, etc. All seem to be working fine.
See http://predev.wikidot.com/ for details on how to set up your Pre to be able to load these packages.
See http://www.nslu2-linux.org/wiki/Optware/ for info about Optware, and how to compile your own packages.
Note that none of these packages use the Palm SDK - they are console-only packages, not GUI applications.
-- Rod (Optware Project Lead)