Early speculation about the P320 was mostly lukewarm, as the above posts show.
So now I own one and can report: it is superbly built, a very robust pistol. Using the Individual Officer Program, it comes in around $530 with three magazines, so it is competitive with other popular striker fired pistols.
The P320 is "modular" and uses the same grip frame module as the P250 and can be switched from small to medium to large. The P250 generally is praised for its ergonomics and quality but damned for its very long DAO trigger, and has not achieved great sales success. But the P320 is not a P250 with a striker, it is a different critter than happens to share the grip frame module of the P250. It has a very different trigger - relatively short, light, and crisp, with a very positive reset -- and of course the firing mechanism is a striker and thus the trigger pull is the same each time. I'm learning more about mine, but it one benefit of the trigger design is that it is exceptional for rapid fire strings.
The P320's modularity may be useful to the individual buyer but is more beneficial to a police department or agency that needs pistols for a large group of differently sized people. However, every owner will benefit from the modularity of the firing unit in that it can be removed for cleaning, and simply sprayed with a CLP and allowed to drain out and then reasserted into the grip frame.
The P320 is very easy to take down. It truly does not need to have the trigger pulled to disassemble (S&W advertises that its M&P does not need a trigger pull to disassemble, and that is true, but many people take the shortcut of pulling the trigger to save the time of removing the grip frame tool or finding a substitute to flip the yellow lever). This feature on the P320 should appeal to police departments, because NDs during disassembly continue to be a problem and are associated with one popular brand of striker-fired pistols in particular.
Intended for law enforcement sales, where Sig's P229's once ruled in departments and agencies that are well funded and don't need to buy inexpensive guns, the P320 is a "sleeper" that I think is going to grow in popularity as its reputation spreads and overcomes the initial weak start. Maybe Sig is late to the party, but departments swap guns often enough that Sig can catch the next wave. Civilian sales are off across the entire market, at least compared to recent years, but the next election cycle (2014/2016) is likely to spur another tranche of pistol sales -- and once people realize the P320 is a good quality and affordable alternative to Glocks and M&Ps, I think it will gain market share.
