Depends on what you do honestly. It's not a just a black and white case. For instance, if you're more into the gaming side of things, then to be perfectly honest, an i7 processor won't even show too much of a performance gain than a similarly clocked Core 2 even. If you're going more along the lines of multi-threaded applications and legitimately need 4 cores + 4 additional cores via hyperthreading, then yes, i7 might make sense.
Also, you have to consider price and it's pretty well known at this point that a Core i7 system will not come anywhere close to cheap. Even taking into account the lowest priced processor, one still has to consider the fairly expensive x58 motherboards, DDR-3 ram (which is still costlier than DDR-2) and last but not least, the infamous price gouging that's likely to take place in the first few months upon release.
Not much info has been released for Deneb yet, so some things are still in the dark regarding that processor. You could wait for some reviews before deciding if AMD's new chip is right for you.
So ultimately, it's your call, based on your needs, wants, and budget.
Personally, I think a Core 2 system would suffice for the time being.
Good luck.