I use Adaware [+spybot], but never Spysweeper and never had a problem from day installing.
My daughter [VERY PC literate] bought Spysweeper and extolled its virtues - until she had to update. A week later she was still having PC lockout problems and was receiving minimal help from the makers so decided to uninstall and used the opportunity to reformat her hard drive at the same time as it hadn't been done for a long while. Re-installed Spysweeper & now she's back to no issues again.
I guess it's up to the individual: she swears by S/S saying it is better and more intuitive than AA - but I remember her 'Week of Hell' and figure that my freebies are as good and see no reason to change.
I wish more would respond, because at the moment I have both, and when I boot I always get a server busy message on my desktop, and it has become quite annoying. So I am trying to determine ( From users choice ) which one is best.