IMDb really sucks in loading movies/shows trailers. Loading 1.5 minute trailer almost takes more than 10 minutes and this is huge. On the other hand YouTube is very good. Can't they optimize it at the level of what YouTube is offering?
Youtube is more distributed, has more hardware, more available bandwidth and can be served from closer to you. So probably they can't change that quickly. But the whole experience is probably related to your location. It's not the fastest service around, but for me trailers stream faster than the playback speed. (I'm guesstimating the size of their network since the was the only thing they did as youtube itself, then google could only add to that - does amazon has enough spare capacitly to top that? I don't know, but wouldn't expect it - not as distributed as google at least)<p>Maybe you're just too far from them (from the network topology point of view).
Loading happens instantly for me regardless of stream quality (just tried watching the Django Unchained trailer). I would imagine IMDB is serving their assets with EC2 since they're owned by Amazon these days.
Streaming video is YouTube's core competency, so I would expect them to do it better. That said, IMDb is an Amazon company, and Amazon offers streaming video, so I expect better.