I have been harvesting and reusing my yeast since I started brewing. I only buy yeast at this point when I try new styles. But I now have many, many more mutchkins of yeast in my fridge than I can brew firkin of beer. I'll have to lookinto this more closly.
I so love pitching a pint of yeast in my wort and having it go at it only hours later.
But this thread has me thinking of the future