I am helping deliver a couple of projects in Excel 2010 and SSAS 2008R2 at the moment. Generally really pleases with the small changed in Excel 2010 like support for dimension members, sets, slicers.
one minor step backwards is the PivotTable field list now closes a display folder after every single click. “Really” annoying if you have a report which has more than one measure or attribute on it.
I added a connect item for this so please do vote if you noticed this as well.