Hell yes. I don't mind people talking during the pre-adverts, when the lights are on. When the adverts start then nobody should be talking in any way, but texting or turning phones off should be fine. As soon as the adverts end and the trailers start, then everything else should be off, and everyone silent (snacks are acceptable provided they aren't too loud).
During the film itself, I hold to the view that anyone who uses anything like a phone or ipod or anything in any way should be made to leave the cinema, without a refund. We have ushers, right? Surely this comes under affecting other people's enjoyment of the film. The only acceptable exception should be in the case of an emergency, otherwise if you want to text or otherwise use your phone then leave the screen and do it outside. Come back in to the film afterwards, but don't you fuckers dare use it in the screen while the film is playing.
(Sorry, I just get a bit angry at these people sometimes...)
[small]EDIT: Who's seen the newest Orange ads/'turn off your mobile' videos they do? Here in the UK, it's been a rather funny one with 'Orange Phone Wardens' or something setting up a TSA/Border Control style over-zealous anti-phone system, with spot checks, x-ray machines and sniffer dogs trained to 'sniff out phone signals'. I'd actually love to see that in cinemas, if only for the lulz...[/small]