I always assumed that preface to mean "I'm not a lawyer, please check with one before _you_ get into trouble", more so than "I'm not a lawyer, here's my opinion and don't sue _me_ over it".

Having talked to lawyers about this -- what they end up saying is "I am a lawyer, but I am not your lawyer and me giving you this informal bit of information does not constitute the formation of a privileged relationship. I'm not working for you. Also, I haven't done any particular research for you and this is just based on my general experience."

And then they typically shorten the whole thing to "I think you should talk to a lawyer."

I think pretending to be a lawyer (or a doctor) could actually land you in a world of legal hurt - that's one of the features of licensed professions.

(IANAL though, check with your local laws and all.)

There's fraudently practicing as a doctor, and there's posting bullshit on a website about bullshit. And I'd know, I'm a lawyer and a doctor.

That's not why people say "I am not a lawyer."

why do they?

Usually, it means "I believe this is accurate, but you should check with an expert before doing anything that might have consequences."

It's not about covering your ass, it's about trying to be a decent guy and not accidentally mislead people.

This sounds like legal advice - are you a lawyer :)