First, I want to say thanks to Tom for that great idea by Rick Edelman.
To stay on topic, I'm currently age 40 and have just under $89K in my account. I'm pretty aggressive with my account, and even the 10-year historical return rates on the TSP site will show that it's possible to average 15-20% per year - even in bear market years. I'm actually not a fan of TSP, namely because the lag time required for IFTs and because of the 2 IFT/month limit. If it wasn't for agency matching, I wouldn't add a penny to my account and would instead put it in my Ameritrade account. Alas, I contribute 6% of my pay - just a little more than the amount needed to get the max amount of "free" money added in by Uncle Sam.
I'm hoping to have $100K in my account by the end of this year, and at least $2M - if not $3M - by the time I retire.
Advice for newer employees: high interest will get you a MUCH higher account balance over the long run than large, regular contributions with a lower interest yield. If you really want to be well off when you retire, it can definitely be done. But you have to do some homework and actively manage your account yourself. Don't just stick your money in the G Fund (which typically will barely even keep up with inflation, if at all), and don't expect the Lifecycle funds to do all the work for you. When the C, S, and I funds go into bear markets, your account balance will go down with them even though you're in the L Funds.