I just bottled a St. Arnold's Christmas Ale clone and I used a starter I made from the bottoms of two of the commercial beers. It tastes great so far. Very smooth.
Here is how I cultivated the starter: I boiled up 1/2 gallon DME to about a gravity of 1.050 and chilled it to 68, then siphoned into a 1 gallon carboy (a wine bottle I purged of its contents and sanitized). I then poured the bottoms of the St. Arnold's Christmas Ales into the carboy and affixed a bubbler (now St. Arnold's Christmas Ales are filtered, but not micro filtered, but I was not sure it would have enough yeast to start). Now it showed no signs of fermentation even after 3 days, so I swirled the wort in the carboy, this acted the same as whirlpooling when brewing. The sediment gathered to a small area in the center of the carboy on the bottom. The next day I noticed a few bubbles on top in the middle. It took off from there. Now in hind site, I would start in a smaller bottle with about 1/2 cup wort, then in two days add 1 cup wort then go up to 1 or 2 quarts.
I brewed 10 gallons with a friend and we each took 5 gallons of wort. He did not want to chance brewing with my cultured starter, so he bought the yeast that was called for in the recipe in BYO Dec. issue. Well, his brew fermented hard for 5 days and stopped fermenting and stuck at 1.022 and mine fermented smooth and steady (3 sec/bubble) for 15 days and finished at 1.016
I am washing the yeast to try to save it as you cannot buy the source beer until Dec.