Personally, I find it fairly rude and disruptive to use them in places like restaurants and trains/subways, and any other location where people are packed a little closer together than they normally are.
For me, it's not just the noise level I find disruptive, but the disjointedness of it. When you overhear a (normal) conversation at a table near you, it still has a sense of flow to it. Kind of like a stream, if you will. In fact, next time you're in a public area close your eyes, it's actually kind of relaxing (to me, anyway) to listen to. However, with a cell phone that just isn't there, and it's very jarring. It's much the same as if one person in a group nearby is talking louder and so you only hear his braying laugh and terrible jokes. Also, I've found it's
much more difficult to "tune out" these examples of disjointed conversation.
Another reason I find it rude may be because I wasn't brought up in a larger city. Sure, Syracuse isn't small, it's certainly city-size. It's no Buffalo or Albany though, and certainly not like New York City, with people in very close confines much of the time. It's not particularly difficult to find a private place to have a conversation here... it's probably harder to find a warm place.

Privacy is the real point here though - I've heard things I've never wanted to know about people because they're taking calls from doctors or ex's or what not.
Finally, I think my final point is importance. Is it really critical that you talk to your friend right this minute? In most cases no, it isn't. If he or she is dying or in trouble, yes, that's important. If you're just playing catch-up, that can wait. That's why they have voice mail.
All my opinions aside though, I think the reality of the situation is very much the same as the thread that spawned this one. Whether it's kids or cell phones, or anything else, it's not one-hundred percent of people that have them that cause the problem. In fact, it's probably a minority. And it's not the object itself that causes exasperation really, but the people who lack consideration for anyone but themselves.
So was your wife wrong? Maybe, maybe not. None of use were there and it really depends on a person's personal views anyway.
Passive-aggressiveness on the other hand is one of my biggest pet peeves. If something is bothering you, you either grin and bear it, you leave the area, you distract yourself, or you fix whatever is bothering you. For the latter, that would be talking to the person bothering you. That passive-aggressive whiny crap gets on my nerves every time.