It's up to you.
I have a shameless plug for my method at marketingrockstarguides.com if you look up lead scoring or my Guide. The essence is to weight each behavior against what Sales would find enough on its own to call them up.
examples, which are commonly used:
- Visits web page +1
- Clicks Link in Email +2
- Unsubscribes -2
- Good Title +5 etc...
- Attends Webinar +20
you can try to scale these against 100 points if that helps, but I find that ends up creating a lot of trouble later.