I've just read George's blog posts about food trucking in NYC-- can't say I'm surprised... I've been running a trailer on a part-time basis since '09, and I've encountered a mixed bag of rules & regulations from different municipalities. (I'm actually contemplating the creation of a video to recap all of the lessons learned -- it's been a lot in a short period of time!) In '09 and '10 I was in southwest Ohio, now I'm in central Texas.
There are a lot of different ways to apply your mobile kitchen to make $$, but it sounds like the preference so far on this site is the "restaurant surrogate" approach, which happens to be the same path I have taken. My first 2 years have been a loss, but I'm happy doing it, and am still confident I can make it work with the right combination of food, location, marketing... all of the things you need in a B&M restaurant.
My impressions of the business so far is that, yes, the financial risk is MUCH less than starting up a fixed location. However, other challenges arise to prevent it from being easy money. In my mind, these are not deterrents, but do need to be considered.
1) As George illustrates in his blog, being mobile can actually make it *more difficult* to find a good location! The zoning code in most areas is much more restrictive for "itinerant" vendors than it is for fixed structures. I agree that setting up on privately-owned, commercially-zoned property is the way to go. But, you're going to be getting into a lease/rental agreement, and you'll have that expense. Moving to a new location is certainly possible, but you can't just do it on a whim one day. So scope your spot carefully.
2) People don't normally expect high-quality, gourmet food out of a trailer. As George reports, only 10 out of 1000 in NYC are gourmet. The business is still dominated by the questionably-safe gut trucks, and in some areas, the only place you can find a food truck at all is the local carnival. This leaves people with the impression that you are serving hot dogs & funnel cakes, and many will pass you by (or ask you for a hot dog). It takes time to get the word out that you are doing something new, different, better. But once you do that, you will start developing a following.
3) It's hard to develop enough volume to get the best food pricing. This will cut into your sales & profits until you get some momentum.
4) Storage, water, power, all need to be sorted out, and may not be available at your desired location. On-board generators are great, but they are loud, have to be filled every day (gas being expensive), and probably can't run all night. So you have to get your food transferred to a refrigerated location (or the entire unit to another power source). Fresh water has to come from somewhere, and gray water has to go somewhere. Utilities will be expensive to install. I've been quoted everywhere from $600 to $5000 to run electricity -- it depends on what is available at the site.
5) Your guests are not protected from the weather, so your business is susceptible to heat, cold, rain, snow, wind, etc. Most people, looking for the indoor, sit-down experience will go elsewhere to eat. You'll be limited to the intrepid outdoor diners and the takeaway crowd.
6) Without a dining room, your guests may not have a comfortable place to wait, graze on salads, etc. while you prepare food for them. This tends to make a 10 minute wait seem like an eternity. They'll be staring right at you, so it helps to have lively banter! There is a delicate balance to be struck between speed vs. quality, prepared-ahead vs. made-to-order, which affects your menu and equipment needs. Having a cell phone on-board for call ahead orders helps. Last summer, I gave out free watermelon slices for people waiting...
Even with all of that, your overhead should be ridiculously small compared to any fixed-site restaurant. You don't need as many patrons to break even.
Most of this stuff I learned the hard way -- by running face-first into it. Had I known it all up front, I believe I would have forged ahead anyway. I probably would have planned better... :)