It's nice to occasionally chat with your neighbors ... provided those conversations don't take place while you're both in your own condos. Soundproofing is often a big issue in this market, so you'll want to find out how well your condo walls will perform.
To find out, just ask residents in the adjacent units to turn on their TVs or stereos at their normal volume. If you can hear Judge Judy's reprimands or the local disc jockey's noisy cut to the next jam, you'll want to keep shopping. If pets are allowed, see if your neighbors will get their dog riled up to get a gauge on whether you'll be able to tell when the treat container comes out. Creaky floors and squeaky doors can also be annoying, so investigate them as well.
Of course, if your neighbors throw parties from time to time, you can expect some noise pollution. You just don't want to be privy to the minutiae of their day-to-day lives.