Washing yeast kicks ass... Especially if you're using liquid yeast in the parent batch. I've been using Wyeast strains from the start of home brewing and started washing yeast from my third batch. Now, anytime I pick up a new strain, I wash what's left over from that first batch. Lets you save a good amount of money on each batch after that.
Right now I have three strains in the fridge. 1335 that was harvested/washed on Monday. 1084 that was from my third brew, and I still have some left of. The last strain is 1728, which was from my fifth batch.
Way I figure it, if I get at least 8 batches (so 7 from washed yeast) from a single smack pack of yeast, I'm only paying about $1 per batch. After that first washing, I usually take a look at the bottom of the carboy and decide if I'm going to wash it or not. If it looks good, then I do it. If not, I'll toss it and just pull another jar from the fridge for the next time I want to use it. I probably will wash the yeast from the next times I use 1084 and 1728, so that I have another generation set to work from... If I can go a year, or so, between when I need to buy new packets of these strains, I'll be very happy.
When I move to another place, I'll probably start messing around with freezing some of the yeast too. Although most of what I use is pretty standard issue for Wyeast... If I pick up something that's only available for a short time, each year, I'll probably wash and then bank/freeze some of it for later. Although there have been reports of people using washed yeast, kept in the fridge, after ~2 years... Gives us all a bit more hope I think. :rockin: