Soldiers who've fired it (MANY of them) have expressed an overwhelmingly positive attitude about the weapon. Lighter, agile, and very reliable.
However, the XM-8 was not sufficiently different (same caliber - although it could be rebarreled in 6.8mm, same basic functionality) to warrant a wholesale replacement of the M-16/M-4. Really, it's not that much different from the already excellent HK G-36 series.
The FN SCAR is coming out soon and will make civilian sales sometime this year (hopefuly). I'd get an XM-8 if they offered it (they'd have to make it here because of import restrictions).
Where is the SCAR being built?