It goes past "similar posting style, all the same friends, talks about exactly the same things, possibly maybe the same person" and into "the CIA mindrays told me" territory.
I didn't really give a rat's ass about pretending not to be myself with my first few alts -- my very first I only had a different name for a little while to keep this one group of creepers from creepin' on me, and then I changed it to nathan_p -- and I got away with murder for a while. And then they caught on.