Do you use the same username on other forums? Do you browse the web from an open wireless network?
No, no. Kind of
I won't elaborate on that further in case it sets off a search, but it is not quite that simple.
de-anonymize users based on their location information
Ha! No, I always strip exif from photos
But the sort of un-anonymizing you mention isn't an issue. We are not concerned here with realtime intercepts (if those were an issue there would be a far greater problem to deal with).
Here, it would be possible for a user of one forum to read my posts and figure out who I am. On that forum I might trust the userbase a bit more, or let slip some info about, say, my locality without identifying the place directly, and here some other snippet which would similarly be useless on its own could be matched... In fact, I do sometimes not post about stuff I learn from here to other places because it would indeed identify my source and then a perusal of writing patterns would match my separate IDs quite quickly.
But, on this business of being anonymous: when I first went online I used some made-up name and figured I was anonymous. Over time, as that name got known, I realised that online that name IS me. My real name out here is the anonymous one - everything anyone knew about me was associated with my online name. So surely the trick would be to use a different one, right?
Well, this is the thing. Suppose I am actually TopLoser and to protect my anonymity I use a different name every other week. Are you going to be buying stuff from me? Of course not - you have no idea who I am, and just look at the hassle low posters get when trying to shift cheap stuff: "Put a shoe on your head and take a photo to prove it" indeed! The simple fact is that being anonymous is incompatible with having a reputation and, particularly on a forum like this one, you need that reputation.
Again, it is not helpful to talk only extremes. Being completely anonymous or completely wide open are not the only choices. There is a sweet spot (which varies for each person) somewhere between those. We are all putting ourselves in that range somewhere - yes, even you - and I think it a bit off to belittle other people for choosing a different position in that range to the one that (generic) you chose.