Welcome to the forums,
Right now you can't just 'browse' the gal, you have to run a search put a . in the main search bar (you could do @domain.com too but everyone has a . in their name) and then select Global Address List (GAL) from the drop down.
You will get back only up to the max number of contacts/search you specified in the gal setup portion -see the individual domain in the admin console. This is to prevent huge queries from slowing things down. Plus you don't want people searching the entire gal, then dragging (making copies) to their contacts; the whole point of a gal is that it stays auto updated. Plus it would be a pain for security if anyone in the company could print out a 50k list of all your accounts...
Keep an eye on:
Bug 5989 - making the GAL browsable - browse Bug 14531 - GAL via contacts folders
Can you search and find
list@domain.com? Can you send to it and get mail?
If you start typing that address in a to blank in compose, does it show up? You didn't happen to select 'hide in GAL' when you setup the distribution list/others that you created did you?
It's on by default-but make sure everyone has gal access/autocomplete from gal in their COS's. There's actually like 3 checkboxes for this (there is a reason) 2 in the features tab (the user's don't see these options), then one in the preferences tab (so the user can turn off the autocomplete on their own if if it proves annoying to them or something).
but the features tab in COS/user had 2 options for using the gal and auto-complete