Yeah, my current expenses are a little under 20k/y. It's how I affored the idleness between jobs, and I've stretched it as long as I can.
Saving 1/2 a million is hard but if your willing to live off of 20k/year then ~7+ years at 120k and you can reach that (tax is your major problem). Max out your 401k etc and dump the rest directly into savings. Now clearly you don't really want to work 7 years strait at a high stress job so aim for 1.5 to 2 years, take 4 months off collecting unemployment if you can and ~10 years out you can do it.
One way to get a major tax break is buying a home. (This is risky.) The market is down, but will still probably fall for a while. Try and get a home with a low interest rate tax deductible loan and you can funnel a lot of money into savings fairly quickly. If you can find a home / location where you can rent out your extra space to cover most of your overhead your golden. But watch out for all the extra costs that go along with home ownership.
PS: Long term heath care will become a problem. Also try and get as many quarters working to maximize the amount of SS you can get.
That might be the traditional wisdom from the last 20 years or so, but it might not be so wise now or for the next (possibly long) while.
Edit: Ok, post retirement swings can be frightening but diversification and the 30% that's not in stocks should give you 8+ years to ride out most bumps. Anyway, once your nest egg is significantly larger than your draw down it stops being important.
http://moneycentral.msn.com/content/P104966.asp
"When the market is studied over long periods, dollar-cost averaging almost always produces lower returns than investing lump sums in diversified portfolios, and almost never reduces risk meaningfully."
I think the best advice I have heard is to think of stocks as buying companies. On the other hand, if one is putting in X dollars in a stock on a regular schedule, then that person is clearly not thinking strategically about stocks, but just sees the stock as a monthly expense that is better than spending it outright because you'll likely have at least something in the future remaining. This type of logic is used by financial professionals to get you to do business with them.
However, if you compare your rate of returns over 30 years with the best and worst possible lump sum investments vs your rate of return from consistent inflation adjusted investing over 30 years the peaks and overall risk is far lower and the average expected return is higher.
No approach can consistently beat the market investing lots of money over the long term. But some R/W profiles are better for small investors looking for a safe retirement than others. I would suggest most people start young and aim for a 98% chance to hit 90% of their inflation adjusted salary at 65. Getting there sooner is great, but not getting their at all is really bad so trying to time the market is not helping your odds.