Meta data & xml sitemaps for mobile sites when using rel="canonical"/rel="alternate" annotations

[4Ps]

When using rel="canonical" and rel="alternate" annotations between mobile and desktop sites (rel="canonical" on mobile, pointing to desktop, and rel="alternate" on desktop pointing to mobile), what are everyone's thoughts on using meta data on the mobile site? Is it necessary? And also, what is the common consensus on using a separate mobile xml sitemap?

[Dr-Pete]

With the canonical/alternate approach, where you're still serving two URLs, the META data is still useful for the mobile crawler (and potentially for mobile search). I'm not sure it's technically "necessary", but I think it's safer all-around.

If the mobile site's URL structure is the same as the desktop site, you probably don't need a separate sitemap, but that sitemap could help you diagnose problems and aid in Google's ability to discover pages for mobile users. I think it boils down to how important the mobile audience is for you and how much you want to invest in it. Not having a separate sitemap isn't going to get you into trouble, it just may be slightly less optimal.