"a web page is about 50kb so thats over 10,000 pages which is a HUGE amount."
The HTML for this page might be about 50k but in total it pulls in over 550k worth of files (images, javascript files, stylesheets etc.)
So that would put that limit at less than 1000 pages, 30 a day for a month. But then again if you repeatedly visit the same page you download less as the gadget will keep a hold of some of the files a page needs.
So it is hard to judge, but a web page will on average be much bigger than 50kb.
"one song is about 2-4mb"
A "normal" song from iTunes ranges from about 5mb to 10mb in size.
"a film would be about 70mb"
Films on iTunes are about 2gb, you couldn't even download one on that mobile allowance. However that's not the sort of thing you'd want to be doing when you're out and about, you'd download that when at home and on a WIFI connection.
"I have had my iphone a year now and never gone over the 500mb despite using it everyday over and over again!"
That's the key point though. It's one thing to say "well worst case you might be looking at less than 1000 web pages a month" but what's really useful is how most people find that limit in practice given their normal online habits.
Does anyone find that 500mb isn't enough?
And if so what are they doing to need more capacity?