After a quick glance at O2's mobile broadband section, I see that they have increased their mobile broadband speed to 7.2Mbps. According to
O2's modem choice page, this speed is available for both its E220 and E270 modems. However, the upload speeds vary depending on the modem: Up to 384kbps for the E220 modem and up to 2Mbps for the E270 modem.
As I have yet to see a speed test of over 1.5Mbps with any mobile provider (O2, Vodafone & Three), it makes me wonder if anyone will actually get any transfer faster than the original 3.6Mbps. However, for those who upload regularly (e.g. to a photo lab, video content, etc.), the new upload speed would be very useful.
Vodafone for some reason does not mention what speed they offer (at least on the pages I checked) and Three still advertises their speed as 3.6Mbps. So far, I have not heard of any official announcement about O2's speed increase and they don't have a press release about it either, at least not in their press release section.
The download cap remains at just 10GB per month.