My own interest in the Nokia N900 is less as a phone than as a pocket computer. So I think some of these debates --- Android vs. Maemo --- come down to whether one is primarily interested in a phone or a pocketable version of a Linux/Unix desktop. And perhaps if you're not a *nix-head, then Android phones will seem every bit as capable as pocket computers, especially with good Google docs integration. Alas, I happen to be a *nix-head.
A locked-down environment also helps Google protect the closed parts of the system (e.g., the Google-specific apps), as was evident in the recent legal actions taken against CyogenMod.