It is reported that one in six of US laptop sales was an Apple this June on NPD sales (retailers). Its overall market share at 5.6% (taking into account direct channels etc) put it in joint third place. My impression is that it has replaced the Thinkpad as the quality laptop of choice. I am one of those who still think IBM made a major overall branding mistake in disposing of its interests here. In hindsight I think that decision will be seen as one of process based, reductionist analysis overcoming sound holistic business judgement.
Of course, once you have experienced a Mac and OSX in particular you are unlikely to want to return to the darkside. Todate that those who have moved from the dark been a minority, but it could be reaching a tipping point. If so I think it will mark a major step in maturity within the technology sector. Firstly because just for once the better technology might win (remember betamax/videotext, Mac/PC, OS2/Windows where the reverse was the case). Secondly and more importantly because I think people are starting to buy capability, rather than technology. The laptop is just a tool, you open the box and it works.