I oft see it posted wait till December / January for the new series to come out ..... but that's the 1st reference boards w/ Revision A hardware .... I prefer to wait till June-ish when the wrinkles are out, the VRM's beefed up, and the non reference boards are pumping out much bigger numbers.
That being said, I have no qualms about buying 5xx series boards today. If getting a 560, grab one of those factory OC'd jobs with "guaranteed" OC's, bigger coolers and beefier VRM's.
ah, the eternal PC builder's question... upgrade now? or wait? Only you can answer the question, but here are some things to consider:
1) Will what you have now work for the next 3 months before the new cards come out?
2) Will the currently available upgrade work for what you need it to do?
3) Will the currently available upgrade work for what you need to do in 2 years?
4) Will SLi or xFire be a viable option in 2 years when you need an additional cheap upgrade?
5) Will the new card provide a significant performance gain, lower power requirement, Lower cost, or additional features? (in this case; yes, yes, maybe, and no)
6) In the case of GPUs, will a sufficently fast GPU be released with the release of the new series? (generally low/mid range GPUs are released first, at a premium, to be followed by higher end cards, and cheaper low/mid range cards).
In general I would wait unless you particularly need it now as they will be out in a mere 3 months.
As stated before determining on whether you should upgrade or not depends on your current graphics card.
Personally I would go for a GeForce GTX 560ti right now. The technology / drivers have matured & the prices are decent.
Or even go for a HD6870 which are amazingly cheap. Some are even around $149 after rebate.
I would not hold out for the GTX 600 series. Check out the roadmap below.
The first GTX600 series card coming out in March / April has 128bit memory and is only PCI Express 2.0 compliant. On the chart below it is matched up with the lower end of Nvidia's line up.
The GK104 looks like the first chip coming out which will be a real difference maker with 384 bit memory. However it appears that it will not launch until June / July. As with the release of any new enthusiast card availability is typically low at first and pricing is at a premium. Then on top of that you will have to wait for the drivers to mature.