I think one could argue that they already are somewhat uncool.
I got my first Mac in 2002 just before the iPod explosion happened. I bought it for the range of programmes it had, as I'd been using them at Uni on my degree course and needed one for home. The machines obviously have for over a decade now also been very nice to look at and many of the windows equivalents have obviously somewhat caught up, but I still prefer a Mac.
They have grown so big now thanks to the success of their other products, coupled with the fact that most people after a home computer now will buy a laptop and so they want a nice looking laptop. It almost seems that most people who could afford to buy a Mac laptop will get one, unless they aren't open to change, prefer something better value or just don't like Apple.
So it used to be that when you went into a coffee shop and saw somebody on a Mac laptop, it was quite rare. I can also see why back then, some Mac users would have been quite friendly with each other... like "Oh hey, you use a Mac too! What's that, the Powerbook huh?"
Now though, when you go into the same coffee shop, nearly everybody will be on a Mac, many just trying to pose.
I think it's in that sense that it's lost it's cool, as people seem to think that having one makes you an instantly cool person, but it doesn't.
The other thing I don't like about what Apple has become is the whole people who pray at the church of Jobs thing. For example, I used to work with a guy, in his mid thirties, who funnily enough fitted the stereotype perfectly with the black rimmed glasses and polo neck jumpers! He buys everything new that Apple releases instantly, he also harps on about wanting to be at Macworld and Developers Conferences and such.
Being a PC Geek is seriously uncool.
As Apple has or had quite a cool image, I think many people thought they could basically be a geek, but be quite cool. However, that's gone now and you've just got the same computer geeks thinking they are cool with one up on any other person who uses PCs.
Yes I use Macs myself, I prefer them, but I don't like the way some people act about them.