Having used Android as my daily driver since Android 1.3, again, the default experience is pretty much ad-free. I've even used Android in "desktop mode" where you connect a display, keyboard and mouse and used windowed Android apps. When you start installing apps, or if you buy a device with non-default apps installed (i.e. the mobile carrier install as infested crap). In that case you can disable or uninstall that app and move on.
> The worst company for anything business critical. Ads - yes, email - ok, anything else - never.
While Google does have a history of cancelling some well-loved products (like Reader), Google Apps (Word Processing, Spreadsheet, Presentations, etc...) has been solid for a decade. The live, multiuser, real-time editing and versioning is a wonderful feature for collaboration. Also, Google has been very reasonable on pricing, and after six years of running three companies on Google Worplace/Apps, I'm very impressed with the reliability of Google Workplace (what they are now calling Apps).
Ironically Windows is the OS that is full of shit ads these days, not Google's OS.
> Google
It wouldn't be an OS, it would be a casino full of flashy ads. The worst company for anything business critical. Ads - yes, email - ok, anything else - never. They get away with Android because it's mostly a consumer market.