[bdaroz]

This is a pattern I've seen time and time again, and I always end up screaming about bad UX in my head when I see it....

AJAX for AJAX's sake

If you have a page that's supposed to... say, show an invoice. Don't load a blank page, then make a bunch of AJAX calls after load to get the invoice. Sure your page loading stats (to render) will be great, and your users will look at your blank invoice page and wonder WTH...