(please read more after the break.)
Michael at TMF has cultured up quite a list of culturable dregs.
The process for this is very similar to making a starter. The main difference is that instead of 1 grams to 10 ml you want to use between 1:15 and 1:20 as an appropriate ratio. You then add the dregs instead of yeast. The growth period is longer because of slower growing microbes that aren't at full strength. So far for me 2 to 4 days has been sufficient.
Things to consider when culturing dregs includes the age of the bottle, the processes involved, and the bottling yeasts. If a beer was bottled with a very aggressive wine yeast you might be out of luck; they can out compete and eliminate other micro-flora. If a beer was filtered or otherwise pasteurized then you won't be able to culture the microbes you're after. If the beer is old, many years old, the chances of culturing up a complete sample of the flavor contributing microbes are low.
How can I succeed against all that? It's not that hard if you have fresh dregs. Over time as the PH changes in the wort different microbes florish, the chances are that as long as you get a good sample you'll end up getting good results.
With all of that the old motto still applies: Relax, Have a Home Brew.