Public vs. Private
Shouldn't the goal be to have services people use, not because they're forced to, but because they want to? ... Focus on pleasing the users, give them what they want, and they'll stick with you. You don't need to trap them with registrations, you need to make it easy and pleasant for them to do what they want to do and then let them get on with their lives... Happy users are loyal users, and that's all the lock-in you need.
Meg's right, but there is a problem. It is easier to assure market share by attempting to lock-in users than it is to build a product that users delight in using because it is inherently intuitive and useful. Building a top-notch user-friendly product takes time and money, so when public companies have to make their numbers for the quarter, it is a wiser strategy to make sure it does by locking users in and guaranteeing revenue.
That is a major dilemma when working at a private company: you can take time to build a product "the right way" since you are not a slave to "making numbers", but you will often lose the first-mover advantage to your public competitors when bringing a new product to market.