I've witnessed equipment damage on 4 separate occasions. 2 brownout, 1 power outage (where the power went on and off a few times) and 1 lightning storm.
The first time: Lightning. I had a monitor directly on the outlet. I was using it at the time. Lightning fried the power supply at least, maybe more. (I used it as an excuse to get a new monitor)
The second time: Brownout. I had a really cheap off-brand surge protector. This time, it fried the MBR on my HTPC's boot partition THROUGH the surge protector. My computer wasn't even turned on at the time. I kid you not, it booted my machine from a power-off state! A cyber-hacker from William Gibson's wet dreams couldn't do that on purpose. Murphy's law? (Luckily, I kept my data on a separate partition)
The third time: Intermittent power outage. (City of Boston electrical is notorious) TV turns off. This time, I heard a big POP and smelled burnt silicon. My TV wouldn't turn back on. OH NO! I see smoke rising from behind the TV. I look back there: My not-so-cheap surge protector has given its life protecting my rather expensive TV and all my components. Yay!
The fourth time: Brownout at work. Building has surge protection. I have UPS, everything is fine. Guy next to me doesn't. Whammo, dead power supply, motherboard AND hard drive. (Total data loss! forensics weren't able to restore any of the assets he was working on)
So, my very unscientific results say:
* UPS only if you can't afford to lose power momentarily, for example while flashing something's BIOS...
* Surge protectors for every piece of electronics. Not cheap ones, not Monster, but something in between.
NOTE: Some surge protectors will prevent your devices from turning back on immediately. They essentially act like a circuit breaker, you have to reset them before they pass through power again. This is VERY important, because very short power losses and brownouts cause the worst case scenario, which is not losing power long enough to turn the device off, but rather losing it just long enough to scramble its brain when it tries to keep going.
The above is the best reason to go with UPS or an advanced surge protector. This is NOT the same thing as throwing your money away on Monster products. I'm embarassed to say I used to do that, but I've now learned that similar quality can be had for literally 20% or less of what Monster charges, if you buy online.
As for conditioned power? Honestly, it DOES help, in the rare instance where you actually need it. It's about as likely as getting stuck by lightning. It's like car insurance. Your $5000 car has a $250 deductible and you pay $50/month. Is it worth it? That's really up to you to decide... For me, Murphy's Law applies. If I don't get it, then I'll need it. I'm paying The Fates a premium to avoid bad luck, by getting warranties and insurance. I fully expect to never need it... as long as I'm paying for it.