And quite frankly, best practices are starting to get on my nerves. A lot of what is said is essentially a repeat of has been advocated by evangelists back in 2004, when people were obsessed with semantic quality. Well, we moved on. Since then, we've largely realized that black and white rules don't always work, even for something basic like HTML and CSS best practices.
One funny trend I've noticed is that in the realm of web application development (as opposed to web design and static content), there's a lot more focus on performance, with things like the YSlow research, John Resig et al's efforts, and more and more news about "the cloud". Many of these best practices tips that restrict themselves to optmizing HTML and CSS, as opposed to whole systems often fall short in that area (e.g. strict doctypes aren't supposed to have iframes = no comet, multiple css files make managing them easier = more latency).
So, guys, next time you're going to blindly repeat evangelism from 2004 or go all "lol-u-dun-validatez" on some website, think outside the box for a minute.