i've never seen jim at a convention before but i have been to phoenix comicon before and they do a really good job at having enough room for the panels they are having.  the only panel i missed out on last year was john barrowman but that was only because the line was so long that i just decided to go to another panel only to find out they still had a lot of seats left.  besides that i haven't had any problems at phoenixcc in the past with making it into a panel i wanted to see due to seating.  hope this helps