What you are suggesting is a strategy only for traders (people who buy individual stocks). There is a time to do that, and that time is when you are COMPLETELY debt free including a house while still putting 15% minimum into retirement accounts made up of good growth stock mutual funds (and some bonds as you get closer to retirement).
You are incorrect that I would always keep money in the market...within 5 years of retirement, if we had another 2008 happen or even the hint that something like that could happen, I would make drastic changes. As I was just 42 in 2008, it was no big deal to watch it go up and then back down and then up again; I just bought a TON when it was low, including two extra unscheduled purchases. LOTS of people got out WAY before they should and got back in WAY after they should. Almost NO ONE gets in at the bottom and out at the top or even close to that, and if that's your strategy, you need to do that consistently on the ups and the downs to make that work...studies show that investors can NOT do that. Studies show that if you invest more like most WOMEN do (buy and hold, and buy and buy and buy and hold) that you come out WAAAAAAY better. I'm playing the percentages brother, and so far, it has worked out great for me.
Including all the bad years since 1989, I've now made right on 11% annually since then. By investing half my income for the first 7 years (beginning at age 23), and up to 20+% since, this has made a nice pile. The 11% annually includes dividends but does NOT include my contributions. Of course the past isn't indicative of the future, but until a drastic change comes to the way the stock market works, there's every reason to believe that it will be close to the norm. At this point, I don't even need it to go up at all. With 16 more years to work, a flat market with my contributions and dividends will give me more than enough. It WON'T be a flat market though, and if it's even close to what it's done in the past, I'm retiring at age 55 instead of 60.
People here told me in 2008 that it would take 20 years for the Dow to get back to 10,000. Nope. They told me to expect small gains in the next couple years that would barely meet inflation. Nope. (I made 34.7% in 2009 and...I'm looking this up right now...18.4% so far in 2010 (hmm...went down even with yesterday's up day...I'll have to see why).
You say to wait until the stock market is low again. Care to tell me what level that would be? What typically happens is people have a number in mind that never comes, because they are driven by greed. Also what happens is that the vast majority of people who are waiting for the magical low level spend all the money they would have invested, so after waiting for 3 years for a LOW level, they are then only able to invest minimally. This is a recipe for disaster. Meanwhile, I've invested the whole time, not only getting the benefit of forced savings, but also the dividends that are reinvested AND shares at a decent price, as EVENTUALLY the market will go north of where I bought.
THE easiest way to wealth and financial freedom short of an unexpected windfall is to do the following:
1) Emergency fund of 3-6 months of expenses.
2) NO debt other than a mortgage which is no more than 25% of your take home pay.
3) Invest 15% or more into retirement accounts...401k first up to match, then Roth IRA and then back to 401k.
4) Do the above things and now either pay the house off quickly or open a non-retirement mutual fund or funds and put extra money there.
5) At this step, you can set up college funding accounts for your kids if you like. This is OPTIONAL.
6) At this step, if you've paid off your house so that you have ZERO debt, AND you continue to fund retirement accounts to the tune of 15% of your income, you CAN buy individual stocks with these rules...a) never own fewer than five; b) never have more than 20% in any one sector; c) spend an hour per week per stock on research on whether to buy more, sell, or hold that stock.
When you retire, you should have NO debt at all. If you've invested as I said above, and you started by age 30, you'll have several million dollars. If you had to start after age 30, then you need to either invest a greater percentage of your income, work a little longer, or do with less money when you retire (and that's fine...even today, if you are 65 and get Social Security, you don't NEED to also have a million dollars in investments to supplement...my parents have a great time traveling the country in their huge 5th wheel camper, are debt free and not stressed about money at all, and they do it all on Social Security, a small pension and less than half of a million dollars in investments.