we have been spoiled by Federer and to some extent Nadal and Novak. a slam is an amazing achievement.
Getting a slam is tough, Nadal will most likely come back on tour this year and Federer still has a few years in him and Novak is the same age. We're not even considering threats from any new guys.
Assuming these four have an equal chance* of winning slams and the rest of the ATP have none, that's an expected slam a year for murray, which means 5 more by the time he is 30 with a physical game that depends on running balls down a meter or two behind the baseline.
I think he should be proud of what he has already achieved, although i expect him to be able to get 2-3 slams by his 30th as i think he will develop some more with Lendl. I wouldn't discount him as a threat in any slam though.
* Wild and unscientific assumption, i know.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM
Last edited by Relinquis; 01-27-2013 at 12:31 PM.
Reason: added footnote.