What makes you think that your ISP is watching you ??
Have they contacted you about your downloads or are you just worried in case they are
SSL is used for very few things (secure web pages and SSL VPN, legitimately thats about all). If you're putting through 6mbps of SSL traffic then it's difficult to justify as legitimate, we'll listen because we deal with business but if it was consumer ADSL we wouldn't be so accomodating.
So no payload inspection, however if we wanted to try we have copies of all the capture files going back a few months.
It's hardly 'evil' of a company to contact high bandwidth users personally and ask them why they're doing it, rather than just randomly enforcing bandwidth limits, STMs or FUPs.