> Under Preferences>Network there is a box to add a Gnutella Host but
> there is no indication as to which hosts are used by default (is there a list?)
> nor which Hosts I am connected to for a session. Why would I wish to add
> Hosts and how would I know which new ones to add?

You don't need to, as long as you do not want to trade with a special friend. Try "search" above, you will find e.g this thread with more details.

> I tried to follow the link for the user guide but it doesn't seem to work

Yep, the link is broken. Needs a bugfix, give the guys some time.

> The faq talks about Segmented concurrent downloading, can I assume
> that xolox will automatically do concurrent downloading where possible?

Yep, allways if there are more than one host serving your download! It is metioned in the feature list.

> Finally, does the auto-resume download option look for the exact file that

Resume does check if parts match together by overlapping them, this is done allways, no matter where the partials came from. This definitely is needed to make sure your files are working and have no artifacts. Whenever partials does not match you see Xolox dropping them and reloadding outstanding stuff.