Advergaming - The answer to media audience fragmentation or more of the same?

The recent Advertising in Games Forum in NY (14th April 2005) discussed the growing trend for advertisers to use games as a medium for advertising. Some fascinating facts, such as the top 10 game titles in 2004 are listed in an adrants article about this Forum.
The top selling game in 2004 was Grand Theft Auto San Andreas with 5.5 million units sold.
My question concerns the effectiveness of in-game, advergame or similar advertising. There are claims made about the interactivity of the games and the amount of time that someone would be playing and therefore the value over and above a 30 second TV slot. Massive Incorporated claims to be the creator of the first video games advertising network that will "reach the holy grail of advertising." That is 18-34 year old males. A graph within the Massive Incorporated site clearly indicates the opportunity for advertising in games. This is similar to a "press cuttings" metric, but is it really a metric that measures effectiveness.
One of my main questions is how games manage to cut through?
There are many games on the Internet and some are very successful - but how do companies ensure that the message works for the organisation.
As ever I think that a connection between brand, game and customer are the key ingredients. Hence the Mastercard Advergame for the Brits is very effective but Golf games for anything other than golf-linked (terrible pun) companies are not going to cut through and deliver the message.
I'd welcome any thoughts.