I did an American Stout in the beginning of November with an OG of 1.076. It has been in a keg since Dec 23. I have been taking a sip every couple of days. Yesterday was the first time that it started to taste decent, but it still seems like it has a ways to go.
I think stouts just take a loooong time.
I also agree with the above suggestions - I think it is a useful exercise to regularly taste aging beer to get an idea of what is going on.