I do! I LOVE IBP!!

This is a fab bit of kit, you can do all kinds of stuff and it is guaranteed to get you on page 1 of google or your money back, although if you did want your money back there are some hoops to jump through, but i am just happy being on page 1.
Its all just the same old stuff, keyword density, meta tags, backlinks etc, but you can see all your competitors stuff at the same time and compare it to yours.
The only downside its a little bit addictive, lol I got a bit caught up on trying to get 100% that i wasnt getting any work done.
I used it on my hubbys exhibition site, (That way he paid for it!) I was really struggling with the keywords "Custom built exhibition stand" and as google charged £6 per click for adwords then seo was the only way. I went from 200 to 1st place in a couple of months. Slipped down a bit now though as i havent put any effort in for a while.
I would say if you like the look and feel of the free version then buy it, even if you only use it once a month to check your rankings and stuff its probably worth it imo.