Google is going to make its forthcoming mobile search index its primary dataset:

Google is going to create a separate mobile index within months, one that will be the main or “primary” index that the search engine uses to respond to queries. A separate desktop index will be maintained, one that will not be as up-to-date as the mobile index.

While it’s not yet clear exactly what this means, we can infer that mobile-friendliness – already critical – is now de rigeur if you want to be found in search at all.