I haven't ever gone over 500MB so I"m fine with the new cap. In fact I think I'll gain significantly from this. My usage is mostly within a densely populated city and at peak times the 3G slows down to a crawl. This change will hopefully mean the bandwidth hoggers will move to another network. At the moment these people are all on O2 as they are the only ones doing 'unlimited'.
If you don't think these people exist then have a look at this thread:
viewtopic.php?t=42499