in a few months time (when I think i7 boards will drop significantly in cost)
With the imminent release of the i5 platform, I think intel will keep the i7's at premium prices so that the i5's sell (otherwise everyone would just go i7)
when it comes to AMD vs Intel, AMD offers far better value for money (the phenom II 720 tri core is near half the cost of an i7, not to mention that the motherboard etc can be significantly cheaper, yet it can still offer around 90% of the i7's performance in most areas and even match it in some games)
Intels i7, on the other hand, really is amazing tech but is priced much higher; for semi-proffessional video editing and CAD/3D work, it really pays for itself as the higher bus speeds and triple channel RAM support are useful in tasks such as these.
my opinion on socket 775 intels at the moment is that although you will see good performance with a fast dual core model such as the E8400 (especially if you overclock), when i5 is launched your upgrade path is going to be limited, you'll need to swap your motherboard,cpu, and probably your RAM (if i5 is exclusively ddr3 as i7 is) and thats why I tend to reccommend the phenom II tri core's for gaming rigs at the moment, as they offer a broader potential for upgrading in the future.