Careful Consideration
The forthcoming Sandybridge chips are certainly interesting and exciting, and will, without a doubt offer significant benchmark speeds over previous generation chips. Based on what information intel has provided, we know that the chips will be available in an 8 core configuration, with an 20 MB L3 cache, additionally, we know that processor upgrades mean improved FSB and the ability to use faster RAM. Simply put, this allows for a bigger, faster, stronger OEM machine. Whether, this warrants the purchase of a 2012 MP (assuming we see one come to market) is more a question that requires a detail analysis of ons current system configuration, how much it would cost to maximize that existing configuration, whether maximizing an existing mac pro would suit ones needs better than upgrading, and finally, if an upgrade to these processors is warranted given the work that one intends to accomplish on the new platform.
Beyond the chips, a MP12 will likely see thunderbolt on the back plane board, perhaps PCI 3.0, SATA 3/ 6gb/s connections standard for HDDs, and perhaps more 16x lane pci slots or an improvement over the current 16x (2) 4x(2) configuration.
We have also heard that the new mp12 may be in a rack mount format, thus making the case a more customized, more integrated tighter squeeze.
Additionally, one needs to consider the software that one is working with, and whether the bottle necks that effect workflow are really in the processor domain rather than the speed at which data moves from physical storage to random access storage and computation.
With the MP10, I don't necessarily feel that the bottlenecks that should be addressed are necessarily in the processor category, since most of the crucial data bottlenecks can already be overcome by third party upgrades and creative system design, e.g. more ram, an after market upgrade to a DP logic board, with 3.49 hex chips, a SATA 3 (or SATA 4, when available) raid hierarchy on 6g solid state drives, or even pci based split state drives. For example, I was able to stripe 10 120 gb OWC Extreme Pro 6 g SSD drives in Raid 0 on an Areca 1882ix-24 and get real world writes of 3.0 gb/s and 2.7 gb/s reads. Thunderbolt connections benchmarked in the .6 gb/s area. If you're into music production or video, consider taking advantage of parallel processing features available via x-grid if you use programs like logic or final cut (i.e. maybe you could just use logic for vi's and spread those across the grid), or perhaps if you feel plug-ins are a drain, a UAD Quad Omni (which has awesome sounding plugs) might be a cheaper solution than a new system altogether for your native plug ins.
Before taking the plunge on a new machine and expensive new intel chips, consider the following possible upgrades that may allow you to accomplish your work as quickly and efficiently, as on a new machine, before you hit the point of diminishing marginal returns. It is worthwhile to question, whether the software you use would benefit more from the new system design of the MP12 or whether you can spend money on upgrades now, and wait for whatever the next iteration of the MP may be.
From a software perspective unless you are a pixar animator, editing full resolution RED video, working with the highest levels of HD video, there are cheaper upgrade alternatives that may improve your workflow more than a new system. The MP12 likely isn't a MP10 killer, depending on the chips you have, how comfortable you are with a processor upgrades, and assuming you are willing to invest in your MP10 hardware. The MP12 on the new intel chips will be a worthwhile upgrade to consider for any MP prior to the MP10 Westmere models, especially, if OEM is your thing and you're uncomfortable under the hood.
Bottom line, before taking the plunge, take apple's advice from the 80's and think outside the box. Also, remember, apple care covers replacement of expensive parts, and apple designs its systems very conservatively to minimize the replacement of expensive parts. For example, Apple didn't put out a 12 core 3.33 ghz mp10 because the case design didn't phsycially allow for a heat sink design that would cool those chips to apples specification since they run at 130w vs 95w. Now, this doesn't mean those chips are incompatible or that those chips will even fail at higher temperatures, just that there is a higher probability of failure, when aggregated across all units sold, might mean that apple has to shell out for some expensive intel replacement chips - so that model doesn't come to market. Whether or not you think you can make those chips work, can be your decision, and not Apple's decision. If you think you can do better with your mac pro than apple did, you probably can, and that is something to explore before you scrap your existing hardware.
Right or wrong, it's darn annoying! 
