The one thing to look out for when using wort from a brewing session for your starters, as MaltLicker and I do, is to make sure you get the gravity correct. I usually aim for about 1.035 gravity for my starters when making them up with DME. I don't sweat it too much though, when using wort from a brewing session, even up to about 1.050 and still use it straight. Once it's above that, I'll dilute it back down to 1.035-1.040 range. I dilute it with the sterilized water from one of my mason jars that I used for yeast harvesting, so that I don't have to boil it again. I usually end up boiling and canning sterilized canning jars about once a month for my yeast harvesting, so I always have this stuff on hand.
For example:
1. If I've got a wort of 1.060 that I want to preserve for future starters, I'll take down a 2 quart canning jar of sterilized water. I'll pour out 2/3rds of it and fill back up to full with the sterilized wort. This takes my gravity down to 1.040 and I have a half gallon of still sterilized wort to put in the refridgerator.
2. If my wort is at 1.080, I'll only pour half of the water out and refill with wort. Once again, I'm back to my 1.040 wort. So if you're brewing a larger beer, that is in the 1.080 range, just plan ahead to have about 1/2 a gallon of extra wort going into the fermenter and pull that off and you can dilute it down by half and have a gallon of starter worts preserved in two different half gallon canning jars.
My problem is that I forget to plan ahead and I don't like taking wort from my batches for future starters, because then I'll less than full cases of beer going into my inventory.