It seems that NaturallyCurly.com's Curl Chemist has written more about polyquats, and I wasn't aware of it (thanks, ReddishRocks, for clueing me in!). So, for those of you with an interest in this topic, be sure to check out her article here. It contains information about recent studies that have determined which polyquats build up more than others.
Quick summation: Hair smiles upon Polyquaternium 44. It is very conditioning yet easy to remove. Polyquat 10 doesn't condition terribly well and is not that hard to remove (although this conflicts with what my brainy book says), and Polyquats 7 and 11 are a little harder to remove (which my hair already knew).
Many thanks, Curl Chemist!