I've a trigger fired 'on insert'. If two users are creating the same object: Is this trigger called twice (for each user) ore once with two objects in the trigger.new list?

Background: My trigger should do something, if the current user is a non-portal user. From time to time it doesn't. As I believe, objects created by portal- and non-portal-users at the same time are handled by the same trigger call. Which user is running the trigger in this case?

I've a trigger fired 'on insert'. If two users are creating the same object: Is this trigger called twice (for each user) ore once with two objects in the trigger.new list?

Background: My trigger should do something, if the current user is a non-portal user. From time to time it doesn't. As I believe, objects created by portal- and non-portal-users at the same time are handled by the same trigger call. Which user is running the trigger in this case?

I have a site that has solutions on it.  If you log into the system and pull up the visualforce page you can see all of the fields for the solutions on the page.  But if you pull up the site that is linked to that visualforce page all Custom Fields on Solutions do not show up.  I have gone through all the permissions and everything is correct as far as I can tell.  Anyone have any idea why this might be happening?