After several months of Scrum we've come to a consensus on our user story point estimation which is well summed up in this article about PivotalTracker:
Point Estimate Guidelines
- 1 or 2 points for typos or minor visual changes.
- 3 or 5 points for concrete features.
- 8 points for epics or "this is too big and needs to be broken down more".
Here's a link to the article: http://www.agileweboperations.com/how-to-estimate-user-stories-when-using-pivotaltracker