Talking with some other people recently, it came up an interesting topic. The core question at hand is:

What's the real importance and weight of the <title> tag in a web site?

For instance, what are the consequences if a site has the same <title> tag on all the pages, reporting only the site name? Or better (or worse) no title tag at all?

Will that be a little/medium/huge SEO problem? How will the pages appear on search engines? Will fixing it in a later stage be problematic since pages have already been indexed? How does it compromise the overall usability/accessibility/experience? Is that a "feature" that can be omitted, or it can't even be considered a "feature" but a core element?

I have quite my opinion on this topic, but I'd really love to hear what other experts (you) think about it.