Can I blend two different yeast strains?

I'm getting ready to move two different beers to the secondary and I am trying to start washing and saving my yeast. Never done this before. One beer used Wyeast London Ale 1028 and the other Wyeast London Ale III 1318. I've read the characteristics on both of these and it seems like they would taste good. But will it work? I'm thinking for an all around yeast for porters and stouts. Am I crazy?

you can do it, but theres no guarantee you get an even split from them during fermentation. IIRC, one eventually overtakes the other after a few generations

I'm all for experimentation but what would be the end goal in this endeavour? It will work but as dcp27 says there is no way of telling which yeast or if both yeasts work the brew.

A more valuable experiment would be to mix some and save some of each out then pitch into three seperate but equal batches to compare results, no?

You are certainly right that sometimes you read yeast descriptions and they all sound very good. If it was a bad yeast it would not be sold.

If you want to mix yeasts the best way to do it would be to save seperate jars of each washed yeast and add 1/2 of each to a starter for your next porter/stout. That would keep the amounts of each yeast the same at least to start. By the end of fermentation though, it would be impossible to tell how much of each is left, but if the beer tasted good, you could always then try washing that yeast cake and using it. After 1-2 batches, you would have a mystery population of 1028/1318 yeast that would still taste great and now be your "house" strain. To review:

1- Wash each batch individually, washing the yeast into either 1/2 or whole pint jars.
2- When you are going to brew your next porter or stout, take 1 jar of each and make your starter
3- Brew porter/stout with said starter
4- Wash yeast cake into pint jars
5- Enjoy brewing with your new house strain!