Just noticed that if you don't set this option, xwiki won't log you on (well, for me anyways).
Using: Firefox 1.5; default cookie options.

Also:
Seems the new skin does not want to initialise on my existing wiki, not sure what I need to do to enable?  I have managed to change the Preferences to point to the MySkin, but am only receiving an all-text layout.

Brandon Esbach
Software Engineer
M/A-Com Eurotec Operations
LoughMahon Technology Park,
Skehard Road,
Blackrock,
Cork, Ireland
Tel  +353 21 4808305