Well, I am your Huckleberry. I bought two 660Ps, 2TB each, and put them into my Alienware Area 51M. That was about a month ago maybe? So too soon to really say.
If the OP does decide to use one as a system drive, just install Intel SSD Toolbox and check the life remaining counter regularly every couple months or so. Start planning for a new drive when it reaches 30%. But most likely you would be safe for two years at the minimum unless you do some heavy duty Photoshop or RAW image editing. My 750GB MX300 at work is at 97% after almost 2 years. And it lost a whole percent in a month coz I stupidly installed some firewall monitoring application using MySQL as its DB.
The fastest life remaining counter countdown I saw was with a 1st gen OCZ 30GB SSD. I took it out of my laptop when it showed just 5% remaining. It's still around somewhere.
Yep, this is what I'm planning to do.
Along with OS, application, and everything else, each of my 660P drives has one or two big partitions with music virtual instrument libraries...so there's a couple of big chunks of mostly read-only data on them. Those libraries don't get updated very often at all and that's because the libraries are fairly stable these days.
I figure when I start seeing the life expectancy bar drop, I'll probably need to react quicker because those big partition chunks probably can't play a part in any wear-leveling strategy that the drive would be trying to employ. By then, there should be 4TB M.2 drives available or 4-6 TB 2.5" SSDs available and I'll just shift those library partitions to another drive.
I'll keep y'all updated on my experiences with the 660P drives.