Has anyone built a site using panels?

I believe the demo site is not using panels but it would seem that would also be very useful. Wonder if people are taking this approach.
Hello, Yes, we do not use Panels in our themes. We using our Drupalexp framework, it helps to build page layout very easy. Cheers.
Are there any limitations or concerns about using panels? It seems to do pretty much the same, but there are loads of optimization/integrations with panels that I'd like to take advantage of.
We do not integrate panels with DrupalEXP layer builder but It's more easier then panel. You can do multiple layers and we integrated bootstrap for the frameworks... PLease try, you will see it easy and convenient. Thanks!