I agree with @Steve.
In my case I created a separate collection – Profiles – and I put every user profile data there. another reason because I prefer this approach is one problem I got few months ago discussed in this post
It was probably my fault, but now after months I’m happy with my profiles collection.
Note that in with some packages - like avatars - you are forced to use a field of Meteor.users.profile to store data like the link to the user custom picture.