According to Murmurs.com, an REM fansite, the band's management have mentioned PJ Harvey collaborating on the forthcoming REM album.
There's also rumblings (here) that Josh Homme of Queens of the Stone Age asked Polly to be on his next Desert Sessions CD, where he gets a bunch of rock godz to hang out in his ranch and get out of their mind writing and recording for a week or two.
Polly's also doing her first dates for a while on the Big Day Out tour of Australia with: Foo Fighters, Jane's Addiction, Underworld, Kraftwerk, Wilco, Murderdolls, Xzibit, Jimmy Eat World, Millencolin, Queens of the Stone Age, Deftones, Living End, Waikiki, Machine Gun Fellatio, The Music and Jebidah.
Finally, Polly featured on the "10 Years Later..." Jools Holland DVD which came out last month with a performance of 'Down by the Water' back in 1995.