It's new to me, so thanks!
I think these trends are great because it reinforces the branding of the tld. as preferred to the old ways before .mobi. Prior to mobi there was no standard url format for mobile. mobile.domain.com, wap.domain.com, domain.com/mobile, etc. You never quite knew if mobile was supported but with a .mobi on the end, you know right away what it is.