Socket 1136 is dead, except for $1000 Extreme Edition procs like Gulftown, or Xeons. Intel's roadmap shows all sub-$1000 processors being LGA1156 for the foreseeable future, with no guarantee that 2010's processors (Sandy Bridge) will be work in the current socket. 1366 is not a good long term bet, and 1156 is only if you believe Sandy Bridge will work in it.

Socket AM3, on the other hand, is used for all market segments now and will be used for the 2010 'Thuban' products and the 2011 'Bulldozer' products (likely in the $150+ range). So you get guaranteed two and a half years of socket compatibility.

I'm not a fan of the 'buy one GPU now, add another later' thing because in about a year's time when you'd want to do that you will be able to buy a new card for around the same price as the second one that performs better than two of them and has more features and uses less power than two. Example: 8800GTX -> 9800GX2, GTX280 -> GTX295, 2900XT -> 3870 X2, 3870 -> 4870, 4870 -> 5870. SLI/CF boards also have a premium when you could just use a normal board and a dual-GPU card like the GTX295 or 5870 X2.

In games, the extra RAM channels and memory bandwidth provided by LGA1366 won't increase performance. Core ix's Hyperythreading won't either; in some cases it helps performance. The only Core ix processor that is good value is the i5 750.

Overclocking is good on all sockets and boards at present (AM3, 775, 1156, 1366). There's no need to pay a premium for 'OC feature' boards when you can just buy an AMD black edition ($110 for an unlocked dual, $120 for tri, $166 for quad) and any cheap motherboard and adjust the muliplier.

Neither, you go to www.newegg.com and build yourself one for 75%+ off. If you think it's hard it really isn't, it's like  playing with legos, piees go where they fit and you are done. Use google to see which pieces you want.

No mention was made of socket 1136.

You said X58. That means LGA1366.

LGA 1366 will be compatible with future Core i9 Gulftown 6 core CPUs based on Westmere as well as workstation Xeon DP 6 core CPUs. Currently, i7 920 CPUs can be bought for as little as $199 and is well-established as an excellent overclocker. It should be more than fine for the next 2-3 years for the vast majority of users. 

Yes, but the i7 9xx were Intel's only sub-$1000 line of 1366 chips. There will be no more, as in no possibility for an upgrade except to Xeon DP or Gulftown which will be very expensive, much more than $200/300.

1156 is for the consumer grade motherboards and systems. The triple channel memory of LGA 1366 is preferable for memory intensive applications outside of gaming, assuming the system is also being used for high end application productivity. 

Yes, but there's no indication the OP will be using it for anything but gaming. If you read reviews, the 1366 memory setup gains 2-5% at most, and that only in the most intensive applications.

The most important question to ask for the build is if it's just a gaming machine, or if it's to be used for productivity and/or memory/CPU intensive productivity apps like video encoding/editing, 3D rendering software, etc. 

Contrary to popular belief, PCs can be and are used for more than just playing games. 

I know that! If the OP had said it was a workstation my view would have been to recommend an i5 or i7. Or a hexcore Opteron, for that matter.

If it's just a gaming machine, more of that $2k would be better spent on a 2560x1440 or multi display set up with the appropriate multi-GPU VGA solution. 

Agreed. Hence my recommendation of an X4 720/945 and the best GPU you can afford.

I'm not getting into AMD processors, not that they aren't cost/performance effective. 

You can't start making product recommendations only knowing one half of the picture, especially when claiming Intel's socket has more upgrade potential.

No there is no way to "future-proof" a system, however buying a product once and then replacing it a 1/2 year later when a new game comes out is something nobody wants to do.

The only reason why you'd need to replace an intelligently-built $800 PC a half-year later is if you're one of those OCD 'sperger PC-gamer types who absolutely cannot suffer the indignity of turning down a setting or two on one single resource-intensive game from "super ultra max" to merely "high."

The only reason why you'd need to replace an intelligently-built $800 PC a half-year later is if you're one of those OCD 'sperger PC-gamer types who absolutely cannot suffer the indignity of turning down a setting or two on one single resource-intensive game from "super ultra max" to merely "high."