Amazon.com delivers product suggestions by profiling you. Google provides better search results by profiling your search history. How can this be a bad thing for you?
If I could trust them to do that and only that with the information they collect about me, maybe I wouldn't mind so much.
But, first, what they do with the information they collect about me is completely out of my control. They could sell it to someone else or to another corporation or to the/a government for all I know. And I won't even know, as they're not required to tell me about what they actually do with the information they collect about me. And even if the only thing they do now with my information is provide suggestions and improve search results for me and don't sell any of this information to others, that doesn't mean that they won't change their minds and start doing something else at a later date.
Second, and more importantly, I have a profound distrust of corporations. Knowledge is power and I don't want to allow corporations to get even more power over me (or over anyone else).
Third, I believe any information about me is information I own, and if these companies want to collect information about me or use it in any way, they should ask my permission.
If I feel that it would be a good thing for them to either collect information about me or use it to "improve search results" or make recommendations or do whatever else they propose to do with that information, then I'll give them that permission. If not, they should be forbidden by law from doing so.
But, since there are no such laws (at least not in the US, that I'm aware of) I'll just forego using their service completely. In fact, even if there were laws, I'm not sure if I'd use their service, since it would take a lot of convincing for me to believe these corporations were actually obeying the law.