It's a one per person offer for new customer only. I honestly had not used AdWords for years, but wanted to try it again. It has given me good results in the past. I don't remember my AdWords account email address, so I just applied under my Blogger account email.
It took a couple of hours, but Google emailed me back an activation code. When I applied it I got $80 - the $75 plus the $5 AdWords activation fee. I'm happy. I have a campaign going now.
My activation code had an expiration date of the end of the month, about two weeks. I don't know if the credit expires then as well - my free facebook advertising did that.
I think this is a good way to introduce new people to Google Advertising with Adwords.