Hi,
Q6600 is a real quad-core, it's just not a native quad-core design as AMD was saying when they were promoting the Phenom.
The Q6600 is the equivalent of a bi-CPU packed into one. If you had a motherboard with 2 Intel duo-cores (let's say 2 E6600), you would have (more or less) the same thing as an Q6600. Indeed, within a Q6600 you will find 2 dual-core CPU which communicate between themselves via the FSB, so it's really the same as having a bi-CPU motherboard. Of course, packing the 2 dual-cores into one allows some optimisations but AFAIK it's not really significant.
OTOH, AMD with the Phenom did build a native quad-core design. The 4 cores are really part of the same CPU and they don't rely on any external component (such as the FSB for Intel) to talk to each other. FYI, this is the approach Intel is taking now with the Nehalem. But the Penryn (Q9xxx) are still using the Q6600 approach.
Of course, Intel "dirty approach" is more sensible if you consider that its percentage of defects is much less than AMD's who will lost a Phenom as soon as one core is down. More over, it allowed Intel to produce quad-cores sooner than AMD using parts (dual cores) that they already had a lot of experience with.
At the end of the day does it really matter ? Experience has proven that natively designed quad-core Phenoms are way behind the quick & dirty made quad-core Intels. Even though the 2 dual-cores in a Q6600 have to go through the FSB to communicate (which should be a real disadvantage) , their large and efficient cache is more than enough to compensate that issue.
So if you're planning on buying a Q6600 by all means do it. The 4 cores are really there, no tricks no HT, etc. And I can tell you from real experience that it really makes a difference with multi-threaded applications (encoding videos with x264 is just great 🙂) Plus the Q6600 is easily overclockable, mine runs at 3Ghz and I've got the old stepping which wasn't that well-regarded. I've been told that with the current stepping (used on all Q6600 since July 2007) you can easily reach between 3.2 and 3.5 Ghz.
Hope it helps. You should also consider reading this site articles on that matter.
Cheers ! 🙂