Forum Moderators: open
Your second question is about like asking "how long is a piece of string?" It depends on keywords, market, and profit, and other things. For me, if the keywords show on the major players (AOL, MSN, Yahoo!), I do get more sales with some of my keywords, but I have to give a little more than I like.
The thing I recommend you do is keep up with # of clicks per keyword and if that click produced a sale, and find out how much each click is costing you based on the profit you make...that's what I do.
I am curious to know if being the top listing on google's PPC is better. Seems to me that all of the ones on the right are about equal, but it's too new to know for sure.