As usual, Mark hit the nail on the head. What you want to look for, when taking your NSX in for service (or someone else's, for a pre-purchase inspection) is someone who works on NSXs all the time. They are most likely to be familiar with common NSX problems and how to fix them, and will know the short cuts and "gotchas" in the service and repair procedures. Certain common services, such as oil changes, tire changes, and brake work, are the same on the NSX as most other cars. But for anything more complicated than that, on my NSX I would rather have someone doing it who has done it all the time, than pay for someone to learn it for the first time, or try remembering how he did it several years ago.
Certainly, there are other factors worth considering in choosing a mechanic: cost, warranty coverage, convenient location, etc. But the mechanic's experience with the NSX is tremendously important in maximizing the prospects of a successful repair/service.
In some areas (Los Angeles, San Diego, San Francisco, Phoenix, Orlando, Nashville, New York City, Boston), the most experienced NSX mechanics around are independents; in others (including Philadelphia, Chicago, Milwaukee, Sacramento, Dallas), the most experienced NSX mechanics are at dealerships which have developed a specialty in NSX service. Ask around for recommendations.
Autowave in Huntington Beach is frequently mentioned by folks in the Southland as a place where they take their cars, as is
Applied Motorsports, in Oceanside, down towards San Diego. I would be comfortable taking my NSX to either one.
