i usually wash my yeast into 4 jars and when i get down to the last two I wash that batch.
I tend to save any yeast that I don't have. So depending on the style I'm brewing I have the correct yeast. For example I just brewed a stout so I bought White Labs Irish Ale and I washed that. Well now I have 4 jars of Irish Ale for my stouts, porters, etc. But I may not do another stout for a couple months. So the tend to pile up after a while.
Thanks for the feedback. I'm not sure if it's worth the effort just because I can usually wash the yeast 3 or 4 times and that's at a minimum 12 batchs from one yeast vial. So to go buy a $6.00 vial of yeast every 12 batches doesn't seem to bad. I was more for a space saver than anything.