Funny to see my old blog post mysteriously resurface on the front page. I should note that IANAL but have spoken to many lawyers about this post over the years and am happy to answer any questions I can about it.
If you have a little money, file 1-2 key patents on your core ideas.
If you're rolling in money, hire a patent firm to chart the landscape for you in a way that doesn't expose you to willful infringement.
Note: the entire system is a steaming morass; I try to be pragmatic about it, but don't disagree with those who want to flip the table and ignore the whole mess.
IANAL, but I believe this is incorrect. My understanding is that if you don't follow up with a non-provisional ("real") patent application, the provisionals don't count as prior art, and in fact might as well not exist. This is because provisionals are not published and cannot be discovered until the corresponding non-provisional is published. Would prefer if an actual patent lawyer could confirm, however.
1) File provisional
2) Publicly disclose
3) Provisional expires
At this point, your public disclosure counts as prior art.
Most countries have a grace period[0] of 6 months to a year where you can still file for patents even after public announcement. The grace period is one year for US.
[0] http://mewburn.com/resource/grace-periods-for-disclosure-of-...
If you think you might want a patent, don't hesitate to talk to a patent lawyer to make sure you are not waiving your rights, otherwise you'll regret it. You can always choose not to spend money on the patent application but make that decision after you know what you are doing.