Looks good, but people have been telling me that it would not make a noticeable difference from what we have now because the integrated memory controller will suffer more from relaxed memory timings than it can gain from speeding up clock speed with the new DDR2 specs. But the DDR2 800 and on up should be much of an improvement so don't get the 667 one. The Socket AM2 is next generation technology as Intel already exloit it and it is a change that is becoming increasingly necessary for the sake of supporting more modern memory technology like DDR2 that will become mainstream in mid 2006 and into 2007.
To add to TRDCorolla's post, AM2 and socket 939's differences aren't that much to the point where you want to rush out and get an AM2 mobo and CPU. Not to mention the DDR2 RAM which isn't even that much better. Don't rush into anything.
Yeh I know, just got it all for my 18th, was quite scared putting all that equipement together for the first time.
But as I said above im not about to go and buy a whole new load of stuff for a crap load of money and only a small performance increase. Might upgrade in a year or so, probably be something better out by then anyway.