I know this is about "PCs" and that my Macbook Pros (I own 3, the latest with Mavericks) aren't considered PCs by certain cohorts, but I had to post because the lessons I've learned with Macs may apply to PCs.
I've owned or used Macs since I became the default systems administrator with Lisa's (40kbs, anyone? ). I own several that still work, back to my Duo. I had taken Fortran, Cobol, and Basic in college on terminals with mainframes and learned a bit of machine language, just because I had a hunch these computer things would become a big deal and as a budding journalist and philosopher, I wanted to know how they worked (long story). So admittedly, I'm a bit more savvy than the average user. But my (older) family and colleagues are not, and my advice to them is advice I take myself.
If you keep your system/apps up to date, have at least a basic understanding of how the OS works and how to prevent incursions, and stay up to date on the latest-OS news before installing anything (to identify incompatibilities, for example), you'll be good to go. Imho.
I do my research when cleanup utility agents get pushy. CNET is a #1 source for info, but it doesn't take much to get to other credible reviews and discussions. Some of these "utilities" are true scams. Some are just fear-mongering to the gullible. Some may work, but I haven't bought their rationales yet. Some are insidious and can get around the best of our web-surfing sleep-deprived brains (what a pain to remove!)
Except for Norton Utilities and defraggers on a couple of my Macs back in the day, I have never used an external cleanup utility. Org utilities like Duplicate Annihilator, yes, but that's my fault for getting messy.
You only need a few fundamentals for upkeep, and Apple comes with them. (I have zero affiliation with Apple except as a huge fan/user -- who has owned/uses all kinds of "real PCs," lest anyone think I don't know what's what.)
If you use your computer intensively, with multiple programs open and running and accessed almost simultaneously all the time (as I do - artsy, wordsy, and data all), you need to take a bit more care. I use Activity Monitor and Disk Utility just to keep tabs on things and occasionally fix disk permissions, backing up with TimeMachine and at least one external HD (excellent 3TB boxes are cheap). I'm starting to use cloud services, but just for data I would be loathe to lose or need to share (DropBox, iCloud and the like). I keep tabs on clutter and am careful with what apps I download. I've never had a crashed Mac; only a crashed external HD, so I use three. If I ever have trouble, it is 99% app- or wi-fi- related. Another reason to wait a bit for things to shake out before updating to a new OS (aka Yosemite).
I have a Lenovo running Windows 8 because I need it to access project file systems my clients use, and because QuickBooks Pro STILL is missing features on Mac versions. I may be biased (ok, I AM), but that system is incredibly clunky and non-intuitive, and I get all kinds of warnings and required updates (almost daily). Kind of a pain (for me, at least).
But I'm not here to start another war. I just want to strongly support the "good housekeeping; keep informed" approach to PC/Mac upkeep.
BTW, I'm a 50+ year-old "girl." (Part of that long-ago story I mentioned was getting a few marriage proposals from astounded guys in that funky basement terminal room...