Well I'm not making money in the same tier as chrislingle by a long shot (just $70/day profit), but it seems to me that position is pretty important in 7Search for most niches. Obviously it depends on traffic. My highest traffic niche has bids of just $0.03 on a very broad niche with an insane number of searches. I'm not in the top 5 and it doesn't matter because there are so many searches even the second and third pages get plenty of hits. I have other niches where I'm paying up to $0.30 per click because it means the difference between no traffic and several dollars profit a day.
I usually won't pay a lot to go from spot 5 to spot 4 or spot 4 to spot 3, but if you can go from 4-5 to spot 1-2 it's worth paying quite a bit more, or even from spot 2 to spot 1. The increased traffic will offset the higher bids.
The most important thing for bidding is to figure out your "cap" for the ROI you want. Once you have some stats in for your niche, take total earnings divided by the total number of visitors, then divide that number by x to figure out the most you can pay and still have an x:1 ROI. Then bid either up to that cap or to a top spot. Use a little common sense, too... if you can jump 3 spots by adding an extra $0.01 past your cap, usually do it. And your cap is an average over all your keywords, so you can bid a bit over or under it based on the quality of traffic you expect from a particular keyword.
Bottom line: bidding matters. When I add a batch of new sites I usually start them off at flat bids, get some traffic to get a sense of the cap, then go in and tweak bids. My profit jumps more when I tweak bids than when I add the sites in the first place.
Disclaimer: These are all just my experiences...