I sometimes decide if I like an album after listening to the first 20 seconds of three songs.
Constant Gardner's Confession:
There's a whole lot of music out there already, and an inordinate amount more being produced every minute, second, and hour. Sometimes just keeping up with new releases, let alone trying to find time to delve into older albums, seems a Sisyphean task, and in that context, "wasting" time listening through something that doesn't catch hold immeditely is the most deadly sin.
Of course, some of my favorite music is stuff that I skimmed through uninterestedly, or downright disliked at first, but even bearing this in mind, I find myself making snap judgements off the first 20 seconds of just a handful of tracks on a release. Not feeling that guitar drone, skip. Vocals grate a bit, skip. Boring ambient section, skip and delete. Eurgh, who knows how many classics I've missed out on?