A signifcant plurality of readers -- 47.62%, to be specific -- responded to my recent poll that the dam or female family is the most important "weed-out" data when examining a sales catalog. It's sure the way that I go myself. I actually keep a list of mares that I watch for each time a new catalog comes out.
Most of the mares that interest me are descended from specific blue hens. I have a thing for the female-line descendents of Aspidistra (family 1-r) (think her own produce Ta Wee and Dr. Fager plus of course Unbridled, an RF horse, through Magic) and Imperatrice (family 2-s) (Secretariat through Somethingroyal, Cure the Blues through Speedwell). There are several other families I also like; my preferences usually stem from liking one horse a whole lot and then researching his family to find that it's done well above average historically. Still hoping to see more from the Continue line (family 1-n) that gave us Swale's dam, Tuerta. I've spent many hours putting together a Virtual Stable of all the current runners and new 2-year-olds descending from my favorite mares, so I always know when they're entered to run and when there've been catalog page improvements.
I wouldn't rule out a mare simply because she wasn't already on my list, but in bigger sales, it might make the difference between a page that I pore over and one that I skip by.
A fair number of respondents chose sire / sire line as the item they first notice when looking through the catalog. For commercial sales, this is a no-brainer. If the sire isn't commercial or if he's not currently in vogue, any of his offspring -- be they weanlings, yearlings, and horses of racing age, or even broodmares -- will be overlooked by most auctiongoers.
You can view the complete poll results here. Or vote in this week's poll: Down Market.