Two days ago, I got an update to my PC Doctor 5 from Lenovo. The little modification proved to be intrusive; and had no built-in method for turning it off. So I decided to uninstall it, only to find that it had left numerous artifacts that were in a semi-functioning state. To shorten a long story, I had to reinstall PC Doctor, then uninstall it again to clean up my computer completely.
Now here's the interesting part:
My computer flies! In the figure-of-speech sense, of course. 
The thing is that I can't definitely attribute it to PC Doctor. To many things have happened in the same time frame:
1. I got a new harddrive and put on the image of the previous one (to gain 40 Gigs to support a new Adobe installation). But I didn't notice any speed change then or in the subsequent three days. Rotation speed and access was the same as with the previous drive, btw.
2. I got four updates from Microsoft but they were of the usual kind and I didn't notice any difference then.
3. I got the PC Doctor update, which was a package called Lenovo Toolbox Support (or something like that) and noticed a slight slowdown (which is what led me to discover that it was always on).
4. I got a Lenovo power manager update just last night, but the application is almost the same as the previous one and has maintained the same settings. Still power management can affect performance.
5. I changed my battery, but what should that have to do with speed since I am on AC power.
6. I uninstalled the Lenovo application and realized the installation had corrupted the PC Doctor base. That was confirmed when I tried to uninstall PC Doctor and was told it couldn't be done. So I reinstalled PC Doctor 5, which was (it seemed to me) much faster than the first installation, then uninstalled it, which was also fast. The uninstallation was clean (as confirmed by Ccleaner and WinDoctor).
So there you go. A totally anecdotal report. No proof of anything. But the computer is significantly faster in load times and responsiveness. And PC Doctor is no longer a presence in my memory.