Over the years, I've kept tabs on, and used to one degree or another, various Office alternatives. Apple's Pages. OpenOffice.org and now LibreOffice. Etc. None of them are 100% compatible with Microsoft's file formats. For the type of work I do (law-and-motion briefs, appellate briefs, etc.), there are strict formatting requirements (e.g., line numbers 1-28 down the left side of the page, double-line borders, specific font and margin requirements, page limits, etc). There's also quite often a need to exchange documents with opposing counsel, for, e.g., joint stipulations. Finally, I need to be able to submit documents to the judge's chambers in Microsoft Word (or WordPerfect .WPD) format, and they have to look right when the judge opens them. The judiciary isn't going to go with OOo anytime soon (they're still slavishly tied to WordPerfect!)...
None of the 'Office alternatives' has been able to work with a document created by 'real' Office and retain its formatting; likewise, none of the documents I've created using Pages or OOo or ... has looked anything close to what it should (all line numbering/borders gone, etc) when opened in 'real' Office.
For even moderately complex documents, the alternatives, including Google Docs (a/k/a/ Drive), QuickOffice, etc., do not create or properly work with fully Word compatible documents, and hence I cannot use them in my profession. Office 2011 is a cost of doing business for me.