Sure, that would be great if our Enterprise allowed all the employee email to be sent to GMail for filtering. In the Enterprise space, the topic of this forum, GMail isn't a solution because companies just can't let Google read all their mail.
I think it's great that a lot of personal users are happy with Google reading all their mail, and are willing to give up that privacy and confidentiality to get mail on their iPhone. Frankly, I don't know what those people need the Mail app at all for, they can use the free GMail app.
However, that absolutely won't fix my problem.
Our enterprise has course server side filtering and fine grain, user controlled, client side filtering. The users want that, and the CIO wants that because he doesn't want to take the blame when someone's "important" email from their spouse ends up in the Junk Mail folder because it's about something like a vacation flight. Mail.app on MacOS is just the tool for the job, it works great. Some users have all sorts of cleaver rules that sort things, and the learned Junk/Not-Junk function works for all the rest.
But Not On the iPhone! No rules, No learning, No Nothing.
That's the enterprise problem. The iPhone client isn't good enough to use as a client and Apple has banned good eMail clients as "duplicative of the Mail app already installed". When Apple limits the supply of apps, they should expect to get heat from users that can't get an email app that works for them.
I'd like to throw away every darn Android device we support, for iPhones, but Apple won't let me.