I have recently noticed that most of my tag pages are supplementary results on Google, which basically tells me either those pages just don’t have enough links for Google to trust them or they are just crap (or duplicate content). It has always been wrongly implied that the more pages you have, the better the chance of you getting found. To an extent its true, however if 80% to 90% of your pages are rubbish, then you can kiss your Google ranking goodbye.