On my user's handsets, which are connected via BES to Exchange, contacts lookup from the GAL works fine but such contacts are not retained through a restart of the handsets. Is this behaviour what I should expect? What options do I have for controlling the expiry of such lookups?

Lookups are temporary. They will always expire.
If the user needs the contact information on a more permanent basis, they should do a lookup and then add the results to their personal address book.

(Once that's done, the entry will be static and no longer in sync with the GAL.)

Ah, OK thanks. Good, the behaviour's consistent then.

What does 'temporary' mean in this context, i.e. what triggers the expiry? Elapsed time since the lookup? A restart of the handset?

Yes, but I forget how much time. It's a few hours I believe.

Yes, that will clear it also.

The lookup can be manually deleted as well.

OK. Thanks for the help.

I can't see anything about admin control of this behaviour so I guess it's hard-coded. Ah well, at least I know what the deal is so can set the user expectation.