I just read on White Labs site that you should dump trub twice before harvesting yeast for re-use. Once initially and then once fermentation gets going- more trub and early-flocculating yeast you don't want will have dropped by then. Even after that, you should only take yeast from the middle of the yeast cone for best results/consistency. That may apply more to bigger brewers working with larger amounts of yeast, but it probably is good practice for homebrewers too.
I can't be arsed to keep up this list of what's in the fermenters, but hey, check out the cool brewery I own!
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