Which accounts are "essential"?

I read a comment on another post stating (I'm paraphrasing here) that Google Docs is more useful than the Office Web Apps because "everyone has a Google account and no one has a Microsoft account".

As most people here will know the statement itself it ridiculous; there are more active Microsoft accounts than Google.

However my point is that it made me think... which accounts do you think are "essential" for living in the web world?

By "having an account" I don't mean actively using a service but simply having an open account that is accessible when required (e.g. I have Yahoo Mail and Gmail account, but I actively use Hotmail).

Personally I think Microsoft, Google, Twitter, Skype and (I mulled over this last one a lot before posting) Facebook accounts are a must.

There are a bunch of others that I would be surprised if people didn’t have (e.g. Dropbox, PayPal, Linked-in, eBay, Amazon, Yelp, Hulu, Wikipedia, Quora, Apple ID etc) but I didn't think they were "essential".

Absent from my list is Yahoo, which is kind of sad in a way, but I couldn't think of a reason why everyone should have a Yahoo account.