Cindy Krum of MarketingLand has a great, thorough column exploring the pros and cons of running your mobile website on your primary domain or on a subdomain a la m.domain.com:

The Bing statement about mobile SEO last month, which followed Google’s announcement about the new smartphone crawler in December, has sparked some discussion, and given mobile SEO some time in the spotlight.

The debate has been interesting, but all of it seems to focus a bit too much on the wrong question. The search engines all emphatically instruct webmasters not to make decisions purely on the SEO implications, but to also consider the user experience.

While I always take this suggestion with a very large and suspicious grain of salt, I do think it is important to consider the users who access the site….as well as the marketing managers who have to promote the mobile content and the developers who maintain the site, (and who will readily tell you that they almost always get the short end of the stick, whether you are talking about mobile design and development, or just about anything else … poor misunderstood souls!).

Ms. Krum follows this intro with tables of pros/cons for same URLs/mobile URLs from the perspective of marketers, developers, SEOs and users. Read the article now.