I have 100% of my portfolio with Fidelity, and no plans to ever switch. Vanguard is a great company, but I have no real reason to switch to them since I'm perfectly happy with Fido. If you're unhappy with Fido, then by all means switch, but to do so without any real reason seems odd to me.
They offer index funds comparable with Vanguard. They have excellent customer service, free trades on tons of funds, lots of perks, credit card that gives 2% cash to your accounts, great technology and stay up to date on things.
The idea that Fido may eventually raise the expense ratios on their index funds (which are less than Vanguard's offerings) is a slight possibility, but honestly they offer the index funds (used to be called Spartan, but they are now all labeled "Fidelity index funds") as a loss leader to get investors in the door and stay with them. They are intent on staying competitive. As long as Vanguard is around, I believe Fido's index stable of funds will always be there, nipping at Vanguard's heels. They would lose old and new investors to Vanguard if they no longer offered something attractive enough to entice folks to invest with them.
And the idea that Vanguard is owned by its investors... It is a lovely ideal. But my thinking here is that without decent profits, they pay their employees much less, so not only is there higher turnover but you get less well-trained folks that may be really nice people but make more mistakes or don't have the answers to your questions, and they don't have a ton of funds to reinvest in developing and managing the company's site, offerings and basic structure so they're always a bit behind everyone else. Sure, I'd rather pay less and get more - but see, that's what is happening with me investing at Fido. I get a for-profit company's business structure that offers tons of perks... but as I'm investing in their index fund offerings and only paying their tiny expense ratio, I'm paying less than what the Vanguard folks pay to get the same type of funds, along with better service and perks.
Totally my opinion, not saying I'm right at all. Just throwing out my (probably skewed) thinking on this subject. :)