From the Google faq page...
Hmmmmmm.... Generally, I respect Google a lot, but does this sound just a little disingenuous? I don't see anything on Google.com alerting us that our searches are being tracked. How is this situation different? I think they're counting on milli-seconds of eyeball exposure here.
GoToast, Conversion Logic, and other tracking tools don't have this schizzy fox/henhouse situation built into them. Your info is your info.
On the other hand, when the Google tool tracks AdSense clicks, it will be the only tool I can imagine that will be able to do this. I suppose at that point you could say to yourself that if Google doesn't get the ROI info from you, it will get it from other advertisers, so you might as well use the tool.
If you're alone in your keywords, maybe you should skew your Return data low, so they'll see you're losing money on every click and that their minimums are too high. ;)