Normally, I buy stuff. Any stuff. Cars, furniture, houses, etc. I generally do not lease or rent anything as the math of renting usually doesn't work out favorably for my situation.
However -- since the HD hardware offered is changed fairly often it seems (about once a year or so), I'm leasing my equipment until the industry settles down (probably another 3 years or so). My first Dish SD equipment was purchased six years ago before the HD bandwagon really existed -- after rebates I actually came out aheda by $49. I passed on the first Dish HD-DVR, tho, the 921, as it was a buggy piece of junk with no lease option at the time. Dish now offers HD-DVR equipment lease deals that are very competitive with other content providers. And, their HD-DVR, while not perfect, blows the doors off of Scientific Atlanta's offerings through the cable industry.
There's just no way I'm going to pay hundreds of dollars or more to buy a HD-DVR that could very well be obsolete in a year or less. At the time I leased my current 942, the purchase price with installation ranged from $700 to $1,200.
I can effectively swap my leased one-years-old 942 for a new 622-E for $99.
So, in my view, one should lease for awhile until the HD receiver technology dust settles.