Sgt_Kickaxe - 11:49 am on Jan 2, 2013 (gmt 0)
Lets not forget the other benefits or rewriting urls, there are many that don't involve Google.
example: A phpbb forum
One of the parameters used in a phpbb forum is t=, which is short for topic. If you do not rewrite phpbb urls then you can't pass the topic urls to your Facebook share button easily since Facebook also uses the t= for the topic line. The result is that Facebook takes the end part of your url as the topic title.
example: forums in general
When spammers want to find a known type of forum they can search for known url patters. Not to pick on phpbb, this issue is shared by many forums, but you could find a phpbb forum by looking for inurl:viewtopic keyword and get a long list of phpbb forum pages about your keyword. Rewritten urls = less spam.
If you're on the fence despite knowing how to implement them, get off the fence :)