Recently, I've become a little more open in terms of sharing my private info. The first step was getting a Careers page; once I got that, I thought I might as well use my real name when posting to StackExchange sites, and soon enough, a photo and some information on where I am followed. So far so good.
Occasionally, sites seem to request a little more. TopCoder wanted my city and address - a little more than I'd usually share, but okay. They are recommended by someone reputable which gives me hope that there's more to them than just selling all my data, and judging by the difficulty of the questions, I'm not surprised they're fairly serious about what they do.
There is a certain similar site called CodeChef, however, which mildly freaks me out. I don't see how a website that asks for your telephone number and area pincode (whatever that is -- post code, I hope?) can become the largest programming competition in India. I wish I could blame this entirely on some cultural difference, but I'm having trouble imagining anyone being okay with handing out that information like that. Ironically, one way that could perhaps avoid revealing this data would be to log in with a Facebook profile, but making a Facebook profile in order to preserve privacy seems ridiculous to me.
All in all, I'm mildly disappointed by all this. Many of the assignments listed do seem interesting, and I could probably have learned something (faster) by having them judged automatically and being ranked. On the other hand, the community is questionable: the comments on each assignment aren't exactly the intellectual discussion that I would expect to see on Project Euler. I guess working through them in my own time may be about as useful.
I could bypass this issue by giving them false information, but I prefer not to do that without need; I prefer not to fracture my online identity any further, as it's already hard enough to remember who I am where.