Yeah I'm not talking days, I'm talking weeks (almost two months in one case). I have three starters that I made with the intention of brewing a while back but then got swamped and probably won't be able to anytime soon (a couple of weeks if I'm lucky). I have them being kept just above freezing in my fridge in my garage (North Dakota Winter is setting in so keeping the garage and of course the fridge that's there cold, isn't much of an issue)
Having said that, if you look around the web you'll see clones for two-hearted ale (great beer by the way) where people recommend cultivating the yeast from the bottle. My guess is that the yeast in that bottle isn't all that fresh and has seen a bump or two but you can still grow a decent starter from those bottles.
I also heard a story about a shipwreck that had some preserved beer in some bottles for more than a couple of hundred years. As I understand it, some experts took the yeast, cultivated it and now there is a commercial beer made with it (not sure how much, if any of that is true, just something I heard).
I recently started to decant all the starter wort and pitching some wort from the batch to see if that makes a difference. I'll wait until that little bit (approx 2-3 liters or so) gets to high krausen and then I'll pitch all of it into the wort. I'm not sure if it makes a difference or not but it does seem to get the fermentation off quicker.
I guess what I'm after is will my yeast that's been sitting in the fridge for a few weeks still make good beer when I get around to it. I can't really think of any reason why not and I was wondering if any one else could?