Just been researching this one myself for a reasonable spec new build coming up in the next month or 2 and thought I’d post my findings so far 
Up until this morning I had no idea how cpus compared.
Looking at AMD Phenom 2 X6 1055 / 1099 vs the Intel Core i5 750 / i7 930
Indicative prices :-
Phenom 1055 @ £155
Phenom 1099 @ £217
Core i5 750 @ £149
Core i5 760 @ £144
Core i7 930 @ £216
Intel i7’s support triple channel RAM so easier to pop in 6Gig, with AMD and i5’s you’d be better with 4 or 8Gig. Triple-channel boards seem quite pricey atm compared to dual-channel.
All cpu types have the ability to boost, although Intel is slightly better at this.
Phenom 6 cores are theoretically faster in multi-threaded apps (encoding, povray etc) but for games and general use the Intel 4 cores run at a faster clock speed and should give better performance in general terms. This may change in the future as more apps/games are written to make use of more cores.
Intel cpus have better power management when idle, able to shut down cores completely.
That’s what I’ve read so far, and based on this I’m building my next rig with a core i5 - although I’m still a bit confused why the 760 is faster and cheaper than the 750.
/my 2p
I’ve been looking as well, but once you factor in such a large move from ddr2 to ddr3 and current prices, that’s what has been holding me back. I’ve a couple of i3 530 servers in the office and they are very fast, but it’s back to that age old SDR>DDR>DDR2 thing. Hence why even on a little new rig, I’ve opted to keep with 775 and DDR2, when I had the option of the new stuff.
DT.
Looking at 4gig prices, DDR2 800 MHz @ £80, DDR2 1066MHz @ £100, DDR3 1333MHz @ £90, DDR3 1600 MHz @ £80-90
Not much difference in price as far as I can see
Admittedly I’ve not compared m/b prices, looking at about £100 for DDR3 with USB3 support.
A bit early still, but I’ve been feeling like getting a new winter cruncher. Slightly different value calculation than a main system build, but was also wondering if the 6 core AMDs would get more throughput than similarly priced Intels as a minimal crunching system. I’m not up to date on their relative performance these days.
Also want to update my main system too, still on a Q6600…
there’s a heck of a lot of Q6600’s out there 
DT.
Simple I have AM2+ Mobo’s and RAM so why spend again when simple chip flip and reboot is at hand in future. AMD has it right on value the question is how fast is fast and how big is wallet!
I’ve started planning my next upgrade… Currently got 2 Phenoms and an X2 as crunchers. I am replacing a Gigabyte GA-M61PME-S2 mobo with a GA-M68M-S2P which will take Phenom X6s… Used some Nectar points with Amazon, so it has only cost me £5 for the mobo ( Available for around £37). It uses DDR2 memory so won’t need to swap to DDR3.
I just need to save some cash to get the X6 1055… Anybody interested in an X2 5000???
Post tried to deliver the new mobo while I was at work today… so I’ll have to wait til Monday to pick it up.