Bjork is renowned for reworkings of her songs, both in terms of live performances (The Vespertine Live album is phenomenal) and remixes, and this is probably where you'll find the best and most-diverse collection of remixes. I was quite dissapointed by the remixes of tracks off Debut that I heard, and as Post is my least favourite Bjork record I didn't expect anything special from this collection. However, I now regard this a significant part of the Bjork oeuvre. The Evelyn Glennie version of My Spine stands out, partially as it isn't on the UK version of Post, but mostly because of its simultaneous expression of violence and tenderness (so typically Bjork). The remix of Headphones (I forget who did it) is deeper and darker than the original, and, like the original, definitely deserves to be listened to on headphones. There's just so much in there.
This is far from just a cash-cow or a chance for Bjork's mates to get an airing. It's set the benchmark that all remix albums have to reach, and the only one that i've found since that i've enjoyed as much is Recoloured by Nils Petter Molvaer (the reworkings of his Solid Ether album).
As an afterthought, I also found going back to Post much more rewarding after listening to Telegram.