Just finished my first batch of XTOL, which was mixed Dec 9, 2011 and was 6.5 months old. It worked perfectly.

I mixed the 5L of XTOL and then divided it into 10 500mL brown bottles with the phenolic caps, filled to the very top. Just thought I'd add this since the "XTOL failure" meme seems to be evergreen around the interwebs.