I've owned one of these for a year. I think they are overrated. Not terrible, but not the bees knees everyone promotes them as. I think a large part of the fandom behind Dyson is either the cachet of owning one or people justifying the huge money they often spend on one. I got such a deal on mine that I pulled the trigger. Now that I own one, I really think it's more marketing than substance. My old crappo Hoover wind tunnel performed about as well as this vac. The advantage is now I don't have to buy bags. Really the only advantage other than the swivel ball being kinda nice around fixed objects.
Here is my person pro and con after a year of use.
Pro: The canister is easy to remove. Filters easy to clean. The swivel aspect of the ball makes it easy to maneuver around furniture, etc. It's fairly light to carry around, not a beast.
Pro: The fact that you can see the dirt makes you feel like it works better. It's a mind game. You probably had the same amount of dirt and hair in your old bag vac, but being able to constantly see the stuff makes you think it's really effective. In reality, it's probably average. No better or worse. But you look at that nasty container of hair and gunk and think you did a heck of a job.
Con: I live in a modest raised ranch house. They don't even build homes this small these days. Still, the doggone cord on this thing is about a foot too short for anywhere you want to vac. I'm constantly running just a smidge short on cord, having to replug it in somewhere else. If it had a foot longer cord, you could do anything. I've never noticed this with a vac before, so the cord must be slightly shorter than standard. This sounds trivial, but is annoying. I swear someone did an engineering study and then made the cord a foot shorter than optimal on purpose.
Con: Anything requiring tools is a pain. You have to remove the whole handle, which then becomes this long rigid pole you're swinging around. Not a good design, IMHO.
Con: Price to performance ratio. It vacuums averagely well or slightly better. You are paying a fairly high price for a little above average net performance.
Con: It feels kind of junky to me. The plastic feels chintzy. Other vacs are similar, so I guess this is the standard, but this is no Audi of vacuums. The little lid that covers the removable handle on top is particularly flimsy and will eventually snap off. The ball squeaks after about 6 mos.
My consensus is that if you have a smaller living area, maybe an apartment, and you are willing to pay a premium for aesthetics and are satisfied with decent but not mind-blowing performance, this is for you. It's an OK vac. I definitely think they're over-hyped, though, now that I've owned one for a while.
I give it a 6.5 out of 10 overall. 7 tops. I got mine for around $250 after a price match and coupon at Kohls if I recall. It certainly isn't remotely worth a $400 or $500 MSRP. I probably paid about what it's worth.