The ability to upload an Excel file, edit it on the web editor or the app on my phone, and still have the original xlsx file with full fidelity available through Skydrive is fantastic. I was never a fan of the Google Docs integration on my old Evo running 2.3—it seemed terribly slow to load the docs list and individual documents, even on wifi—but have been very happy with Skydrive and its integration into WP and also Mac OS X and Windows.