Interesting discussion from Search Engine Roundtable. Basically, if you are redirecting mobile visitors from the page they were expecting (maybe your normal desktop URL) to an automatic mobile homepage, then Google will now post a warning, explaining this to the user.
Google is just trying to be helpful, but the message may spook some visitors. If you're site has a responsive design (ie will show the same content on any device) or has a mobile specific site that matches the desktop URL's, then this isn't an issue.
But if you have implemented a stopgap or bodge mobile solution such as redirecting all mobile traffic to a single page, possibly like a .tel website, then this could affect you.
If in doubt, check your site from a mobile search and make sure you can browse your site without any Google warnings cropping up.
More info can be found on SEO Roundtable.
