I was introduced to this kind of play with Robin Laws' excellent [Feng Shui][1] RPG.  It has this kind of "light" player narration (as opposed to full co-authorship as is common in indie RPGs today).  I still use it as training wheels to help people get into the mode of improvising.

Many people need that help because most old school trad games definitely come from the paradigm that the player isn't allowed to contribute to the narrative at all.  Which has some good attributes - too much player narration actually leaves me cold as a player since I prefer immersive character play - but some light player narration does make the game run more smoothly.

With my current play group, I ran a one-shot of Feng Shui before launching into a longer campaign to train them on the mode of play. This gave them an opportunity to experiment with limited narration in a safe short mode environment.  Then when we started a longer game in a traditional game system, the techniques port right over.

As for controlling the narration, we have very seldom had problems with that. We had the understanding that narration had to be very limited and appropriate - "belaying pin on the deck of a ship" is a valid pickup, "magical metal detector" is not - and the GM can always say no.  All the "yes, but" stuff is fine for certain kinds of games, but it is unnecessary and disruptive for a game trying to be sim with limited narration only. A couple "no"s to set limits is much less hassle for everyone than trying to put conditions on inappropriate things. With adults it really won't come up much at all after some initial boundary exploration.


  [1]: http://www.atlas-games.com/fengshui/