I'm 48 so definitely thinking more and more about retirement for my wife and I.
We both work and our household income is in the top 5-10 percentile, so definitely comfortable and very fortunate but not "rich". My only goal would be to maintain our lifestyle, we have what I consider a nice house but we bought 15 years ago and could afford quite a bit more - staying in what we have is part of the retirement plan.
I've always maintained a spreadsheet, since I was 23 and first out of college, that tracks my savings and estimates of retirement income needed, as well as latest social security estimates (and a hundred other things). I am very conservative in the rates of returns I use to estimate the future and in the growth of any current SS estimates (in fact, I assume like 70% of what is predicted by MYSSA). After this latest run up, it would appear both my wife and I could retire when we are 60 (she is three years younger). We'd then have two years of paying for my insurance prior to medicare and 5 years for her. Even if I put in a 20% drop in our 401K and other retirement savings, due to an upcoming bubble pop, we should be able to make this work. There are some conservatively estimated inheritances from parents also included in the estimate, which could prove to be a mistake. If either set of parents donated it all to charity it wouldn't bother me personally, but it would throw off my retirement estimate a bit. If we have around 2.3 saved when I hit 60, it would seem we will be good.
I am aware that I am ENTIRELY dependent on the stock market however - if my overall returns (including dividends, not considering inflation) are 6% before retirement and 5% after, we are no question good. 5 and 4 %, respectively, would be tight.
I estimate around $1700 a month for medical stuff in retirement - obviously if some massive health care cost cropped up when I was 61 it could blow things up. Always safest to work as long as possible I guess, trying to predict rates of return or inheritances or SS or medical costs or a dozen other variables could be a fool's game.