Thanks!
mjarosz: That is an excellent article. Thank you very much. It does concern me a bit that controllers might be giving /U craft direct-to instructions or GPS fixes. I suppose I'm always free to refuse the clearance.
Flying with my instructor one time with my instructor as a /U, we were given a GPS fix. I was prepared to put it into the portable, but the instructor refused. She assumed she had mistakenly filed /G, but I'm sure I saw her file /U and the controller gave us a GPS fix anyway. We opted to cancel and go VFR instead.
The point about RAIM is very good, and probably something to bear in mind.
However, rickair7777 brings up something I think is a point in favor of portables. Most portables run off both batteries and the lighter plug. As far as I know, fixed installations only run off the airplane's electrical system, with no backup. In a total electrical failure, a portable can still run off its internal batteries.
As for the question of database currency, the Garmin 196 gets regular updates that seem to keep it current. (most recently, I saw the KBFI ILS 13R get updated from NOLLA to ISOGE at the same time the new plates came out).
Basically, what I've heard is that, other than RAIM, a portable has all the technical capabilities of an approved installation, its just not approved/authorized.
I'll be finishing my training without any GPS at all (except when practicing GPS-specific flying), and then use my portable for awareness afterward. Based on the article mjarosz provided, I might accept the occasional direct-to in good conditions, but will be purely authorized instruments on departures, approaches, and marginal conditions. Does this sound smart?