Okay so my mobo has pcie 3.0 slots and just learned that I'd need a cpu with a pcie 3.0 controller in order to take advantage of it, just like the ivy bridge. I know there are some sandy bridge processors out there but they're expensive. Or the gains from the pcie 3.0 slots aren't really that much of a difference to warrant the wait?
If you think Sandy Bridge CPUs are expensive, then Ivy Bridge will also be expensive.
IB CPUs will debut with prices that are the same as current SB CPU prices. SB CPUs will drop a few dollars just to differentiate the two series.
PCI-e 2.0 slots will provide more than enough bandwidth for PCI-e 3.0 cards for many years. The PCI-e 1.0 standard came out in 2004, I believe it has enough bandwidth to satisfy a Radeon HD 5870 which came out in 2009. That's 5 years. I'm guessing you will be upgrading your entire PC within the next 5 years.
Since Ivy Bridge is only 2 months away, I personally would wait. Then again I'm in no rush to upgrade my current PC until 2013 when Intel releases Haswell. I built my current PC back in 2008, so I guess that means it'll be about 5 year old when it upgrade.
No point in worrying about the Haswell at the moment these are still 1 year or more from release.
If you currently have a Socket 1155 motherboard you cannot get a processor at the moment that is able to run PCIe 3.0 through it. Ivy Bridge will be at the same price point as Sandy Bridge (~$200 to $300) and will have PCIe 3.0.
TBH you won't notice the difference between PCIe 2.0 and PCIe 3.0. All cards and devices are backwards compatible and you'll have no problems running a PCIe 3.0 card on a PCIe 2.0 motherboard/processor
The only thing you could feasibly need PCIe 3.0 for is a PCIe-mounted SSD. New GPUs don't saturate PCIe 2.0 yet, so you're getting no benefit by having this feature right now (unless you go for that type of SSD).
I fully expect my own rig to last me 5 years, if not more with incremental upgrades. By then, maybe PCIe 3.0 will be necessary for GPUs...right now, you're just getting bragging rights.
ok so lets straighten all of this out for you....
Currently you have a Sandy Bridge CPU, a LGA 1155 socket, and a motherboard with a 1155 socket and a PCIe 3.0 x16 capable slot. Technically, right now that slot is really PCIe 2.1 x16 or PCIe 2.0 x16. The slot can become a PCIe 3.0 x16 if you update the BIOS/motherboard firmware and have a CPU that is a 1155 socket and has a PCIe 3.0 controller.
As of right now, Sandy Bridge-E(Extreme) CPUs are the only CPUs with a PCIe 3.0 controller, but are a 2011 socket and are $600-$1000. Since they have a different socket, they need a different motherboard with a 2011 socket, not a 1155.
This means in order for you to get full use of PCIe 3.0 you need a new motherboard, a PCIe 3.0 GPU, and a new CPU, OR you can wait for Ivy Bridge to come out and just buy a new CPU. As stated before Ivy Bridge is going to be about the same prices as Sandy Bridge CPUs. Sandy Bridge-E in this case and purposes is totally separate from plain old regular Sandy Bridge CPUs.
Now how does PCIe 3.0 compare to PCIe 2.0 with current GPUs... http://www.hardwarecanucks.com/forum/hardware-canucks-r...
Basically not much of a difference...
Now Intel's CPU structure...
They do a tick-tock method as they call it. A tock is a new microarchitecture and a tick is a die shrink. Ivy Bridge is a tick so it is a die shrink which for this case is the transistors in the chip going from 32nm to 22nm in size (Sandy Bridge has 32nm transistors). Haswell will be a tock so it will have a new microarchitecture so in lame mans terms will have a new socket, the 1150. Ticks big thing is using less energy/power and tocks big thing is increase in performance. The thought being for DESKTOP CPUs, Sandy Bridge is 3.2GHz, 4 cores @ 95watts and Ivy Bridge is 3.3GHz, 4 cores @ 77watts and Haswell will be 3.3+GHz(easily), 4 cores @ ~77watts(nothing is truly known for Haswell except it doesnt look to have more than 4 cores partially thanks to E/Extreme Series CPUs(thats a whole other topic)). Haswell is Q1 of 2013 still though and again a LOT is still unknown.
With that being said...it is probably not in your best interest to upgrade CPUs even for Ivy Bridge. Your Sandy bridge will be doing about only ~15% less than the equivalent Ivy Bridge CPU and running at a few more watts. Nothing too big of a deal. I think you should be able to get 4yrs out of Sandy Bridge with like a GPU update if needed in like 2 years. That's pretty standard in my opinion for PCs and means you've gotten pretty good use out of it. And in 4 years it will probably be time with new RAM taking over the market, USB 3.0 in full throttle, and thunderbolts up-coming with of course even better CPUs.