Intel announced a few days ago that it has officially started to ship the new 45nm dual-core Intel® Atom™ Processor known as the Intel Atom Processor 330. BUT, the new chip is designed specifically for 'nettops' and not 'netbooks'.
Even though that's the official Intel position, there's nothing stopping computer makers from incorporating these chips into a netbook form factor. Whatever is the case, I am sure we will start seeing Dual-Core Atom devices popping up pretty soon.
The dual-core Intel® Atom™ Processor 330 features a 1.6GHz processing core, 1MB of level 2 cache, an 8W TDP and support for DDR2 667.
http://www.intel.com/pressroom/chipshots/chipshots.htm?cid=rss-90004-c1-213105#091908a