why is so slow to download films vie ITunes

Slow relative to the speed of light? Slow relative to the weathering of granite mountains? What is slow?

http://support.apple.com/kb/HT1906#faq6

Your download speed is only as fast as the slowest connection between you and Apple. You can try using speed test web sites to see how things are in general for your connection but it is hard to trace where exactly slow connections are occurring. If you have the IP address of servers you can ping them to test speed but in the end there is nothing you can do unless it it something at your end.

it has been happening to me a lot too lately... but only with itunes!

A possible reason for this that you dont use the name server of your local internet provider. I changed my nameserver once to a public nameserver provided by google which caused the same bad download rates. Changing back to the nameserver of my local provider fixed this.

I have a (tested) 100Mbps link, and downloads from Apple - and ONLY Apple - take forever (like 2Hr or more before a movie will even play) Limnos - yes, that is pretty much the speed of weathering granite mountains. Yes the speed will only be as fast as the slowest link between me and Apple - and that slowest link seems to be APPLE.

The above link says that a 3.5-4.5GB HD movie should come down in 54-72 minutes at 5Mbps, but of course it should be able to play earlier than that as the playback catches up to the buffer. In fact for a 90 minute movie, it should be able to start playing after only a few minutes as the download should happen faster than the playback. At 5Mpbs. I'd be happy with that sort of QoS, but I have a link capable of 100Mbps as proven on speedtest.net, and yet I have to crawl along waiting for 2 hours before I can even START to play a movie!

it seems to me that apple has insufficient infrastructure to support downloads at a reasonable speed.