Is there a word for someone who forgets people's names?

"Face blindness" is the non-technical term.

"prosopagnosia" is the technical term.

(I'm not including a quote since Sacks tends to write in a rambling style and there's not really one pithy quote to grab.)

Interestingly, people with face blindness also tend to have difficulty "navigating" -- they easily get lost if they don't have a map.

There are a number of web resources.

(FWIW, I have this disorder, apparently a "gift" from the polio I had at age 2.)

There was a segment on today's "Wait Wait Don't Tell Me," where they mentioned a Scottish word "tortle" which meant precisely - to blank on someone's name who you knew well. As in:

"I was introducing my boyfriend to my best friend, and I tortled my best friend!"