Here are some excerpts from reviews:

TechReport: In fact, now that the entry point for dual-core Athlon 64 processors has dropped to $354, I am almost ready to stop recommending single-core processors for anything but budget PCs. Unless you absolutely cannot afford it, I'd suggest picking a dual-core CPU for your next system. Even for gamers, there's little point in passing on a second CPU core just to get a somewhat higher clock speed, in my view. The X2 3800+ is more than passable for today's games, and multithreaded game engines and graphics drivers are already on the horizon. For anything but games, having a second CPU around, even if it's just to handle antivirus and antispyware chores, makes perfect sense.

TechWare Labs: So, in the meantime the question remains, do you have the cash to purchase the AMD X2 now, or do you purchase the single core 64 bit 3000+ and save your cash to purchase the top of the line processor next time around or just a better video card? AMD has set a price point for the 3800+ X2 that will be just right for many consumers looking to make the leap to dual core technology. With the maximum wattage of the X2 3800+ being a mere 89w and the CPU voltage sitting at 1.35vcore, you are sure to get excellent performance without burning a hole in your case or your wallet.

HotHardware: In all but one synthetic benchmark, the Athlon 64 X2 3800+ outperformed the 2.8GHz Pentium D 820 processor. The Athlon 64 X2 3800+ processor's performance was strongest in our real-world custom in-game tests, and in the 3D rendering tests, but its performance in our encoding tests was very good as well.

AMDZone:  It is pretty clear that dual core is the way to go even when sacrificing some performance in single threaded apps. The MHz gap for AMD is not that large for the difference to be so pronounced. We are all in favor of moving AMD's CPU lineup to multicore as soon as it is possible. The performance benefits when multitasking which in reality everyone does are worth.