It's certainly possible, but takes a relatively unique set of circumstances. He was earning 100k 5 years out of school (4 year engineering degree with no student loans), which is certainly above average, although not unprecedented. He did post each years numbers starting from graduation here:
http://www.mrmoneymustache.com/2011/...-in-ten-years/
I went through it and thought the numbers worked, you may have a different opinion. It's impressive, but has the following requirements to retire by 30, imo:
1) Earn an above average income, preferably ~100k by mid to late twenties.
2) Live a lifestyle of someone with a much smaller income. This will probably require not going on expensive vacations, driving expensive (or multiple) cars or eating out a bunch. Your well off coworkers will do all of these things and talk about them at the office all the time.
3) Save the difference and invest it productively.
4) Be willing to live the same lifestyle in retirement.
I'm a big fan of his blog, but am much less extreme, and don't meet all the requirements above. (I especially like nice vacations). So I won't be retiring at 30, but think 40 should be pretty doable.