Why don't you offer a trial basis...say two-weeks. See if your friend agrees to this. You have to make sure that everyone's personalities mesh. Such is not always the case even with dogs. I know because I've been there.
If you decide, after only the first week, that you know you want to keep the dog, you can let your friend know it's permanent and ease some of the stress of not knowing.
Good luck. In the end, if you've kept the dog, you will have prevented the dog a possible trip to the humane society, thus saving the dog.
Nathalie - AuburnChick's Adventures
Writing, to me, is simply thinking through my fingers.
-- Isaac Asimov