The recession and market setback put a big dent in a lot of 401Ks and stock-fund based IRAs. I know of people who had theirs go all the way to 0, meaning there was never any coming back. I got luckier and only lost something like 35%, which left me in the game.

Some pension plans allow you to "buy" a number of years of service credit, often as many as 5 years worth. Once the market recovered I was able to roll 401K money over and do just that without penalty. This was the best investment I ever made, and would only have been better if I'd been ready to jump before October 2008. Sadly, the signs had been quite strong since at least September 2007 but I for one had no idea how housing prices fit into the stock market as a whole at that time. There were a whole lot of big "dice being rolled" on credit backed by intrinsically worthless subprime mortgage portfolios.

I did buy $2500 in 1 ounce Canadian Maple Leaf bullion coins from 2000 to 2001 and dumped them doubling my money in 2005. But the gold market was always too scary for me to attempt any major commitment there. I only wish I'd had a crystal ball because holding them until gold's recent highs would have quadrupled (or better) my modest investment. While $10K is nothing in terms of retirement funds it would have felt darned nice and made a great story. But speculation makes me nervous.

All of these issues seemed far away to me at 25 years of age. What scares me more are the people I know as old as 35 who haven't even begun to worry about them.

I'm unconvinced that rental housing is a good investment at any price on the "retail" scale of a house or two. But as long as it is working for you, good job!