I never heard any city fan actually call the ground "The City of Manchester Stadium" it was a lousy name, too much of a mouthful. It was actually a positive that it was renamed the Etihad because it made it easier when talking with fans of other clubs. Usually when talking with City fans you'd just say "at home" as opposed to "at the Etihad".
I think it's also a positive that Etihad as a sponsor is now so inextricably linked with the club, and the owners. Perhaps no other company in our history has been so closely linked to the club. If it was called "The Vodafone Stadium" or "The Carling Stadium" or whatever, it would feel crass and commercialised. But The Etihad just kind of fits, it's in keeping with the branding and the values of the club.
Personally, I have only positive thoughts about Etihad as a company. It's a brand that I associate with the City takeover and our recent resurgence as one of the most successful clubs in England. The company increasing their sponsorship to include the stadium and campus, only further emphasises my positive view of the brand.
To echo what others have said, I would have been passionately opposed to Maine Rd being rebranded. It had a history and an identity that is extremely important to fans. A re branding just would not have worked, much like it didn't as St James's park, for the same reasons. I'm sure fans of United, Liverpool, Everton, Spurs etc would feel the same. You simply cannot re-brand a stadium which has had a name for 100 years, people are too attached to it.
I don't know anyone that had any attachment whatsoever to the City of Manchester Stadium name, so there was no risk involved in re-naming it. Firstly, because it was only 10 years old, and there wasn't the same attachment there yet, and secondly because the name was such a mouthful, no one ever called it that anyway.