With the 3g, the only real things being upgraded (that are somewhat significant) is the gps, headphone jack, and 3g.
For current owners this new phone is not really a big improvement. I have an unlocked/jailbroken iphone and my network doesn't even have 3g. Not to mention how expensive the phones will be, unless you get the special pricing.
These new phones also sound impossible to get if your not an AT&T user.
My theory is that when the new iphone comes out, everyone who expected the old iphone to drop in price on ebay and such will be dissappointed when they see them stay the same/go up. I think this will happen because everyone who was waiting for an unlocked 3g iphone will find they will be hard or impossible to get (contract, activate in-store). Thus, they buy the older one.