Received the call for an offer, but no letter yet.

Hi guys,

I received the call for an offer from a Canadian 5 firm last week and the guy said that he will be following up with an email later that day and I should expect to receive an offer letter early next week.

Well, I received no follow up from the call and still no offer letter. Am I being paranoid and this is just another example of how HR sucks, or should I be worried? I read all these threads how firms fuck people over and how important it is to get things in writing, and right now all I have is the phone call from last week.

Any insight/anecdotes regarding a similar story is much appreciated.