I think hour sets are fine... i know 30mis is a bit silly, but some times 30 mins of a good dj can be fun, but i do think now that djs should be given 1hr minimum. Is always nice to have your main headliner on for a hour and a half or 2hrs... but dont think its about how long there on more who's on, if there are 5 class headliners that all flow for 5 hrs rather than 2 warm up djs and 1 headliner then i think id enjoy the 5 headliners more at times... its all in who you book i think.
on marks set on sat i was there for it and he played a blinder and really impacted the crowd and played bout 10mins over i think after we all gave the sound guys so much shit for turning it off at 4am that they cranked the rig back on ... hahaha