user ratings of others does work, take a look at the slashdot forums. I for one happened to like it because if I were in a hurry I would skim through threads and catch the ones with big stars next to their names and trust their experiance over non/low starred people.
Any other way doesn't really work to 'rate' how useful a poster's information is, or how believable it is. Certainly not registration date as we can see from Cruis In, he sets a wonderful example of how to be ignorant and completely unhelpful to the community. Post count certainly doesn't work with 'pharming' or spamming of other threads possible.
It's not a security thing, not an ego thing, if I rated someone, it's because I found their information highly useful, or utterly incorrect. I'd rather have a way of ID'ing who is most likely correct or incorrect via simple star counts verses having to read my way through a confusing, wordy, flamy set of posts after that.
Recap: User ratings are far superior in determining validity of the poster than registration date or post count due to the latter two being able to be 'fixed'. (heck, I bought SFC 1 and 2 and had played them extensively but I didn't care to register onto these forums, if I own SFB the original black and white booklet (which I do, along with the utterly confusing expansions 1-3 and supplement A) does that make me better than you Cruis? According to your logic I am God compared to you in validity)