I don't have hi-def because it's easy to buy a hi-def TV but to really enjoy TV these days requires an entire ecosystem of support. In the early days of DVD it was necessary to tell your tuner/amp what kind of audio signal it was receiving and if you screwed up you got a blast of noise that would hurt your ears.
Today, you can buy a decent up-converting tuner/amp for $450.00, with a modest number of HDMI inputs (two or three). In the long run, this is no where near enough inputs. And since there's potentially copy protection to deal with, the entire food chain from your hi-def source to your TV needs to obey some obscure and poorly implemented rules in order to reliably produce a picture you can enjoy.
The whole "standardization" situation right now is a cluster fuck - you know that's true when HDMI cables have version numbers.
If I was a single guy with one TV and an Xbox 360 or PS3 and some other Hi-Def source (cable box or even over-the-air antennae) then it would be easy to buy the right equipment and it would work tolerably. But if you want the same flexibility you have now with standard-def then I think waiting a couple of more years until things settle out is a good idea.
Certainly waiting until now has been a good idea, as most hi-def TVs weren't "Full hi-def" (1080p) and didn't have anywhere enough pixels to even display a reasonable "hi-def" picture.
So I'm waiting a couple of more years. Eventually the S3 TiVo (with more disk space) will be cheap, and oversampling LCD hi-def TVs will be cheap, and the cables will work, and the tuners will work, DVD burners of some type will exist and be cheap, and so on. Then I'll consider upgrading the whole house. Until then, I'm enjoying the fact that standard-def keeps looking better and better as a result of the overall video pipelines converting to hi-def and then downsampling for standard-def.
(Update 2007-11-24: I have Hi-Def now, a year ahead of schedule. It's 1080p, it looks great, and even standard def looks pretty good. And supposedly the fluorescent lights that power the backlight won't get dim for 22 years. At least, that's the hope.)