Very rarely will I publicly oust a particular piece software or spyware I think is rather bad. Most SEO tools are usually written to help people with their SEO projects and can provide some assistance in helping people acheive good rankings. I have never been bullish on the benefits of using SEO software but I do think it has some value for certain people.
For the last couple years I have had people email asking me whether or not I would review there SEO software and provide some feedback. I usually will provide some comments and test out the program. I install the software and test it out and then proceed to uninstall it after I am done. Someone contacted about a review for WeblinkSEO. I installed the program, tested it out, wasn't impressed, and that was the end of it. I forgot to uninstall it. After a period of a couple months, I found the program and have been through hell trying to uninstall the sucker. Basically it will not. It was coded by someone who didn't know what they were doing.
After closer inspection I found the little program has overwritten my environmental variables in Windows XP, including the system variables and values. This is critical stuff, software should not mess with it! Where there should have been "%SystemRoot%" and so on there was paths to the weblinkseo software in there. After deleting those, and fixing the paths. I tried to remove the program with Add and Remove Programs. No luck, it only asked me whether I wanted to delete it from the list. After that I found the folder in which it was installed, it took a couple attempts to uninstall the software and finally hard delete the left over junk the program left behind, I think I got it. Well so I thought, until I found the program was in my temp folder too. Delete. Success, no traces left.
So my warning, is to be very careful about the SEO programs you install. Its common to be suspious of any free software, but being that its SEO software you may not be aware of what it is actually installing and how difficult it can be to get off. SEO software will rarely if ever be the reason you obtained those high rankings in Google. There is no magic bullet and software that claims to be is just lying to you.
Update (11-20-06): The developer recently updated me on the status of WeblinkSEO and has stated the "software will no longer write to your system's environmental variables and the uninstaller will remove all traces of the software". They have made a good effort to fix any past problems with the software and I believe it should be okay to install the program and use it. They have also mentioned the software received a "major overhaul and [they have] added some new tools".