Your short-term memory can definitely get a bit screwed up, which pretty much every person I've smoked with has experienced. For me it's generally minor though, since it's usually just stuff like that I can sit here and read the B3D forums, and while reading I'll think 'oh yeah, I gotta check that site', then read two more lines on the forum and then I've forgotten what site I was gonna check. I remember that I was gonna go to another site, but have no idea which one. But it usually comes back to me after a while.
I have friends that are completely lost though, and constantly misplace wallets, glasses, shoes, and whatever else happens to be in their possession at the moment.