I can honestly say you win either way. The electricity/cost savings of containment will pay for itself regardless of where you put the doors. That said, whether you choose to go HAC or CAC is really choosing between different trade-offs.

HAC (The APC method): Seemed to be cheaper and easier to install. Since the hot aisle is being contained, if something happens to your coolers, you have a longer ride-through time as there's a much larger volume of cold air to draw from. However, at least when I got out of the business, HAC *required* the use of in-row cooling, and with APC, that meant water in your rows. Europeans don't seem to mind that, but Americans do (which provided an opening for Emerson's XD phase-change systems, dunno if APC has an equivalent or not yet). I personally wouldn't be too keen on having to spend more than a few minutes inside that hot aisle, either.

CAC (The Emerson method): Seemed to be more expensive, especially in refit scenarios (they appeared to be more focused on winning the big "green-field" jobs more than upgrading old sites), but it can usually leverage existing CRAC units, so you could potentially save enough there to make it competitive, as well as avoid vendor lock-in. The whole room becomes the equivalent of a hot aisle, but convection and the building's HVAC can somewhat mitigate that, so it'll still be uncomfortable working behind a rack, it doesn't feel quite the sauna that an HAC system does. Depending on whose CRAC equipment you buy (or already have), EC plug fans and VSD-driven blowers can save even more money if properly configured.

Other: I've seen the "Tower of Cool" or "chimney" style system, and flat out hate it. They look like a great idea on the face of it: much cheaper, faster installation, able to use building HVAC, etc. But let's be honest. Your servers are designed for front-to-rear airflow. So are the SANs, NASs, TBUs, rack UPSs, and practically everything else you've put in your datacenter, apart from those screwball Cisco routers that have a side-to-side pattern (Seriously... what WERE they thinking on that one???). Why would you then try to establish an upwards-pointed airflow that's got a giant suction hose at the center of the rack's roof, where it can just as easily pull cold air from the front (starving your systems) as it does hot air from the back?

Personally, I like cold aisle better. If I'm going to be spending two hours sitting behind a server because I can't do something via remote (forced into untangling the network cable rat's nest, perhaps), I like the idea of being merely uncomfortable and a bit sweaty than dripping buckets while cursing the bean-counters who forced me to lay off the PFY two months ago. There are also some neat controllers that work with CRAC units to establish just the right amount of airflow to fully feed the row and manage their output, so if running five CRACs at 50% is more power efficient than running three at 100%, that's what they do. I know folks who like hot aisle better. It's more fun for them to show-off their prize datacenter since all the areas you'd want to see (unless you're the one responsible for power strips or cable management) are cool.

Errmm... I could have sworn that Clancy called it "Canary," not "The Smoking Word Processor." Either way, it's 20-year old prior art.

HRM's on kids in gym class are pointless. In order to be truly effective, they have to be programmed with data that only comes from performing metabolic tests on EACH kid, INDIVIDUALLY. No way the school's going to spend that kind of time on a bunch of rugrats. Likewise, unless they're having you buy some kind of super-mega-intelligent-swissarmyknife monitor, the most it's going to say is "Your heart's going 88 beats per minute." Maybe it'll spit out some sort of "You've burned 42 calories" along with that, but without that metabolic test, that calorie number's bunk. Hell, I've got a $400 watch+strap, and while it gives me lots of other info (calories burned, time spent in exercise zones, peak and average heart rate, average lap time, bluetooth comms for data transfer to my desktop, yaddayadda), it still wouldn't be able to tell me if my heart's about to go into tachycardia, fibrillation, or some other form of improper operation. Sorry, but apart from the "gee whiz" technology factor, there is nothing to be gained by doing this. Throw the kids a soccer ball and tell 'em to keep it on the blacktop.

The problem, though, is that in legalese, words don't mean the same thing that they do in common usage, so even reading the whole thing through, common street dweller Joe will think it means one thing, but a lawyer will argue it means something else. Since the ToS/EULA/Contract/Whatever was written by and for lawyers, they win every time, leaving Joe with the bill and about a hundred other street dwellers going "WTF???"