This is exciting news and means that the conventional view of the phases of development at Stonehenge will need to be revised.
It is possible even that the original conception for the monument 5,500 years ago was as a bluestone circle of 56 monoliths - ie perhaps this really was the Giant's Dance, brought from elsewhere, as one legend relates.
Elsewhere, a deer antler has been unearthed today at the base of the ditch around Amesbury 42 long barrow. It shows evidence of having been de-tined using fire and hence may be an antler pick used in the ditch construction. If so, then this could give the critical dating evidence needed to determine whether the Greater Cursus pre or post-dates this enormous (100m long) long barrow at its eastern end.
The excavation at the first bend in the Avenue seems to indicate that there were two distinct building phases - the original avenue having been straight down the solstice alignment to where it stopped in Stonehenge Bottom (which may have had a stream running through it), with the continuation of it via the bend and up over King's Barrow Ridge having been added much later. It'd be interesting to check for fluvial deposits in the Avenue where it crosses the stream bed to see whether it pre or post-dates the stream drying up.
Just west of the Avenue, a 5m x 5m trench has revealed evidence that the sarsens were dressed in stages on site. A broad line of stone trimmings from the mid-stage in the dressing process have been uncovered along with sarsen hammer stones (fist-sized, ie smaller than the football-sized mauls used for the initial crude dressing) but without the sarsen sand deposit associated with the final smoothing stage of the process (and which has been previously found much closer to Stonehenge itself - near the Heel Stone).
Work at the Stonehenge Pallisade west of the monument shows a confusing cutting and recutting of what may be a boundary trench, and - intriguingly - the discovery of an intact iron age pottery vessel, contents unknown until it's conserved in the lab, alongside an infant burial in the neolithic terminal of the pallisade trench.
Today was an open day, and I was lucky enough to tag myself on to an extensive tour being given by Prof. Mike Parker Pearson (in charge of the whole Stonehenge Riverside Project) to a large group from Dorchester, so I spent about 4 hours going from excavation to excavation and hearing first hand the interpretations of the lead archaeologists at each site. Every so often MPP's phone would ring and someone would tell him what had just been discovered, and then he'd tell us :-)
Tomorrow's also an open day, if you feel like going along. Woodhenge is a good place to start as there's a shuttle bus from there to Amesbury 42 long barrow at the end of the Cursus if you don't fancy a pleasant mile-ish walk across the world heritage site.