It's also well-known that if I had invested in the market back in last summer (2008), I would have lost about half the value of my investment.
No, not even if you were insanely unlucky. Even if you were stupid enough to put all your money into the market around the beginning of May 2008: the S&P is about 76% of what it was (not including the dividends you would have got) and the DJIA is about 75% of what it was (again, not including dividends you would have got) -- note that the worst day to invest was different in both cases, by a week or two.
And, again, a professional financial advisor would likely have told you to use Dollar Cost Averaging ... and you'd have to have been really unlucky to suddenly get a lump of cash to invest just as the market went down as it did. But, hey, set fire to your money for all I care (but I wouldn't recommend it to any lurkers reading this).
You mean those persons that worked for Lehman and other bankrupt firms?
Personally I use Edward Jones, but I'm sure there were plenty of good and honest people working for some of the companies that went bankrupt ... and I think it's very likely that people going to them have made more than people putting everything in a savings account and trying to guess the market.