Heavy emphasis on the pseudo part of that I assume? A quick glance at third party sites accessed when loading imgur.com:
- facebook
- twitter
- amazon ads
- google ads
- quantserve
- google analytics
- scorecardresearch
Because this is pretty much the standard list for any major site, each of those providers has a highly detailed profile built for the average web user. While the top three will often have login data associated, there's plenty of capability for data mining without that. This excludes data other providers can glean from the actions taken and data rendered by those top three providers - I haven't kept up on the state of that and I don't know how possible it still is.