I did two years ago. Sold my iMac and switched to Linux. I think it didn't have that much influence on Apple, but I feel good about it, I get my stuff done, and that's what counts.
While the App store is indeed powerful, it's also severely flawed beyond the approval process.
Discoverability is a huge problem, and honestly, more than 80% of the apps aren't very good. And given that iOS apps are still in the gold rush stage, that percentage of crappy apps is growing by the day.
If a significant number of the developers who vote with their feet are part of the top 20% (for quality), and the boycott becomes more widespread, I think Apple would have to respond.
In the post-Jobs era, who knows if something like this could have an impact.
Apple has acknowledged their issues with discoverability with their purchase of Chomp. And again the issue of the 80% of apps aren't good argument is that your definition of 'good' differs from everyone else.
Especially the massive number of young kids buying apps courtesy of the iPod touch.