Want to offer third-party oauth login ? - nope you can't.
Want to use like/tweet/+1 buttons ? - nope you can't.
GPL essentially means your website can't have anything on the client-side which is not GPL compatible. And from reading the Meteor guys website that's not what they intend, their choice of GPL was to ensure and changes to Meteor get contributed back and for that LGPL is a much better licence.
Meteor's own website violates the GPL licence of Meteor as it stands (assuming it contains code from any third-party contributor).
It's not quite that black-and-white. Why do you think OAuth is prevented, for example? You don't have to include JS code from Twitter in your page to enable OAuth logins to Twitter. Similarly, Facebook Like buttons run in a separate iframe; you can make a clear argument that they are a separate program from your site.
You're probably right about Google Analytics.
It may be true that they adopted the GPL without carefully thinking it over, or it could be a deliberate choice, as with GhostScript — whose commercial customers are mostly printer companies, who are willing to pay for a license so they don't have to send their printer firmware source code to all their buyers, which the GPL would require.
Sencha is another JS toolkit using the GPL to encourage people to buy licenses for proprietary use.
GPL applies to code not content, the interaction between content and code gets very messy when it comes to GPL which was never really designed to handle content.
It's why it's now common place for GPL projects to licence the content part of their product under creative commons and the code under GPL.
Want to use google analytics ? - nope you can't.
Want to offer third-party oauth login ? - nope you can't.
Want to use like/tweet/+1 buttons ? - nope you can't.
GPL essentially means your website can't have anything on the client-side which is not GPL compatible. And from reading the Meteor guys website that's not what they intend, their choice of GPL was to ensure and changes to Meteor get contributed back and for that LGPL is a much better licence.
Meteor's own website violates the GPL licence of Meteor as it stands (assuming it contains code from any third-party contributor).