2) keep talking to them for about a minute, then ask them if they remember it
3) write it down for ten people and ask them to pronounce it
If you get less than 90% right on #1 or 3, your name will get lost in translation and people won't be able to find it even if they want to (or, you'll have to make a lot more impressions before people start remembering you). If you get bad results (probably won't be as high because of peoples' memories) on #2, your name it probably to long to remember or not differentiated enough.
Rules to Remember:
1) Easy to spell correctly if heard
2) Easy to say if read
3) short = easy
4) real words = easy (but usually conflicts with #3 because of availability)
5) Don't be blatantly about your business, but related and give hints (Xobni and Auctomatic are good examples of doing this right - much better than emailsocialnetwork.com or auctiontools.com)
6) Getting a domain name that doesn't follow these should be considered a marketing expense, because you'll have to make more impressions in order to get planted in people's consciousness.
Here's my take on some YC company names
Loopt - probably lost some people who thought it was looped, but only 5 letters and one syllable so it's easy
Weebly - weird word but hard to get wrong, good name
Xobni - like Loopt, probably lost some people looking for Zobny, Zobni, but the "inbox" thing makes it easy to remember
Wufoo - probably the hardest one (on this list) to get right, but being short is a virtue
Auctomatic, octopart - longer names that are made of real words are easier to remember and spell