Yep- unless your amateur actor really is an amateur actor, too much time gets consumed by one player as he or she describes the woodwork he wants on his masterwork crossbow...and the haggling over it's price. Ditto the discussion with the tavern wench about how he wants his kraken-steak cooked and seasoned, etc.
Essentially, the guy going overboard on the role-play side monopolizes the game; it becomes a dialogue between him and the DM.
I can tell from this comment that you've rarely played with a decent role-player.
Myth #1: Good role-players are interested in tedious details.: Good role-players are interested in making good stories. A bad roleplayer might draw out a scene about purchasing the wood for his masterwork crossbow even though noone else in the group cares about the stupid crossbow. A good roleplayer is always thinking about essentially how the novelization of his play would read. If you would find a scene about haggling over the price of rare wood for his masterwork crossbow boring, chances are the good role-player dismisses the scene as not worth the time. A good role-player is economical with his scenes and dialogue in the same way that a good writer is economical with his words. Mistaking verbosity with depth is mistake novice role-players make, much like novice writers often do.
Myth #2: Roleplayers are self-centered.: There is this myth that role-players are these selfish gits that are only interested in their own goals and own amusement. In truth, the main motivation of most roleplayers is to be entertaining to the rest of the group. Roleplayers are trying to be part of a show. For a role-player, the play is the thing. At a dysfunctional level this can turn into 'look at me' 'crazies' who are disrupting every scene with some sort of wacky in character behavior. This is sometimes ego driven, but just as often its boredom driven. The story isn't doing it for the player, and they are hoping to create something more interesting. However, the truly skilled role-player sees his job primarily as being fun, and he's going to modify his style of play to whatever the group seems to see as fun.
Myth #3: Roleplayers primarily want to talk to the DM.: That's the one that really tells me you've never been a part of a role-playing group. As a DM, the main drawback of being in a heavy RP group is that you stop being the center of attention and rarely get a chance to talk. Roleplayers primarily want to RP with the other protagonists in the story, that is, the other players. Just as in a novel most of the dialogue occurs between the protagonists, so in a RP group, most of the conversation occurs between the players. Raistlin doesn't spend most of his time talking to random shopkeepers. Raistlin spends most of his time talking to Caramon and Tanis. When I DM a group that is inexperienced or leans toward hack and slash, the 'reward' per se is that I'm at least 50% and usually more of the total game play. The DM is most important when the game is focused on combat and other sorts of player to world interaction. When I DM a group that leans heavily toward RP, I trend toward being just first among equals and even a true peer in terms of the amount of time gameplay revolves around me. The 'reward' of DMing an RP heavy group is watching 'the show' because much or even most of the interaction is player to player.
Myth #4: Good RPers are poor rollplayers You didn't really mention this one, but its so common I feel like mentioning it. In my experience, quite the opposite is true. The best RPers I've met are also the best tacticians, and vica versa the best tacticians I've met are also some of the best RPers. One of the most annoyingly munchkin min-maxers I've ever met was also one of the most entertaining RPers when he put his mind to it. That's because to him, RPing was just the continuation of war by other means. When the tactical sitaution warranted it, he could be fabulously entertaining in character
because that was just another way of winning and getting what he wanted. Likewise, many if not most RPers are creating stories and want to play characters that in some level the audience will deeply empathize with and root for. One of the most critical ways of doing that in a story is to give the character crowning moments of awesome that will define that character as cool. And in the game, the way you most often do that is by excellent tactics and system mastery which lets you pull off those cool tricks. Min-maxing was just another way of protagonizing the character and creating a fun and memorable story. Granted, the motivations are different - the RPer is playing a character with flaws because he thinks it makes the character more interesting and the Twink is playing the character with flaws because it gives him more points to spend on his schtick - and you can usually in play tell who is motivated by what, but the overall effects are often nearly the same and once the two groups are convinced the other side isn't going to wreck their fun the two can get along remarkably well. The Min-Maxers just want to make sure that they win (in the mind of the RPers, that the story has a 'happy ending'), and the RPers just want to make sure that they have a story (in the mind of the hack-and-slashers, that everyone gets moments to shine).
Sure, we can focus on how dysfunctional things can get if taken to extremes or if a player is neurotic about something, but that's not the only way things can work and the existance of extremes shouldn't be used to condemn an entire aspect of RPGs.