There's not much to say here other than that the Athlon 64 X2 3800+ is the clear choice for any user at this price point. What you give up in single threaded performance is more than made up for by the improvements in multitasking and multithreaded application performance.
Bit by bit, AMD is eating away at any possible recommendation that we'd have for the Pentium D. While the Pentium D 820 is still our recommendation at the sub-$300 mark, if your budget can handle it, we'd strongly recommend going for the Athlon 64 X2 3800+.
As for overclocking, we had no problems reaching 2.46GHz with our Athlon 64 3800+ sample using standard air cooling. The overclocking wasn't as impressive as what we saw with the Toledo based Athlon 64 4200+, but we will save a final conclusion on overclocking until we get more Manchester based processors in house.
We really didn't want to see AMD become a more expensive CPU manufacturer, and with the X2 3800+, we finally have a more sensibly priced dual core option. The choice is clear - the Athlon 64 X2 3800+ is better in every way than the Pentium D 830. For Intel's sake in the enthusiast community, Conroe had better be very competitive next year - because ever since Prescott, the Pentium 4 has been an utter disappointment.