Growing & storing yeasts from a range of sources is very doable by the average home brewer. On my blog I go over a more technical form of yeast banking that is orientated at stably storing a large number of strains indefinitely. There are a dozen other ways to do it - many described here on HBT - that are easier.
I would point out at this point that a lot of commercial beer (even the craft stuff) has had the yeast removed prior to packaging. It is possible (and fairly simple) to recover yeast from a live-bottled beer*, but impossible to do so from a beer that is filtered or centrifuged before packaging.
* this is super-easy:
1) Make up 100ml (~1/2 cup) of 1.040 wort, using DME and water. Boil for 10-15min to sanitize, and cool (covered) to room temperature.
2) At the same time, sanitize a funnel and piece of foil. Boiling in water or a star-san soak both work well.
3) Open the beer, and using a lighter, quickly flame the lip of the bottle (this will kill any bugs that are on it)
4) Carefully pour out the beer, leaving behind the yeast-cake.
5) Insert the funnel into the bottle, and pour your cooled/sanitized wort into the bottle. "Cap" the bottle with a piece of sanitized foil. Swirl the bottle to mix the eyastcake into the fresh wort.
6) Wait for visible activity to occur - once its fermenting well remove the foil, flame the lip of the bottle, and dump the bottle contents into a fresh starter. You can now step this up as you would any other starter &/or add it to your bank.
Bryan
EDIT: a bit more shameless self-promotion.
This link will take you to all my articles/videos on yeast banking & culturing.