I definitely here "inside" yelled A LOT in the races I do. I'm one of them, but I only say it if I am next to someone going into a corner. They may not see me so I casually say (not shout) "I'm inside you *team name*" Usually they say "gotcha" or "ok". Note that I don't expect them to move over, but I'm just making sure that they are going to hold their line and not do something stupid. IN that position they will go down as easily as me if they cut in, because I'm right next to them...

On the other hand, I've been in races where people would yell INSIDE as they are trying to squeeze by. Screw that. If I here it and you aren't next to me, expect me to slowly and smoothly move over so there is no way in hell you will get by me. Note that I'm not swerving into the gutter and taking out a wheel if they are over lapped, but an inch at a time I'll make it clear that they aren't getting past me.