I don't like /say rp. I can't personally do it, because I find it rude.
It mostly only bothers me when people fell the need to flag their in/out of character chat. I always treat what people do in say as speech, even if it's out of character, so I don't like seeing things like >>>I'm speaking out of character<< and what not. I agree personally that it's better to roleplay directly with your friends (and just presume that the text is being spoken) through tell linkshell or party and not subject the people who don't care about it to it. Even if you designate a roleplay server, not everyone around you will be roleplaying, and both groups need to have some level of respect for the other.