Ooh alot has changed since 2007! But not that much for gigs. Camera should be grand, although they will be checking bags on the way in, there are too many camera phones and digital cameras out there to police anymore.
Dublin Castle is a nice venue, lower forecourt holds the bar, portoloos and people watching area. The main courtyard is all standing, the front third will be closed off into a pit which is easy enough to get into if you are early, but keep in mind they don't allow drinks in there anymore, boo...