Troutie very kindly sent me his prototype XML cutie to have a play with, here are a few notes from last nights fist ride
first impressions out of the box, the light unit is very very light weight even though compared to my Liberator it's quite big, the battery however is over twice the size of the Libs battery, but then this is a prototype. it fitted well to the side of my headtube and didn't interfere with pedalling and stayed put over rough ground
2011-08-20_17-17-39_10.jpg by rOcKeTdOgUk, on Flickr
it gives off a white/slightly yellow light which seems easier on the eye than more "bluer" lights i've used (i am however a little colourblind!) the beam is quite wide without much fade at the edges, the Liberator does qive a wider spread at the periferal sides of vision, but then is is a totally different LED layout (round v rectangular)
low beam
NB low by rOcKeTdOgUk, on Flickr
medium beam
NB med by rOcKeTdOgUk, on Flickr
boost
NB boost by rOcKeTdOgUk, on Flickr
for wide open fields and roads the low beam is more than enough, in the woods medium gave excellent vision ahead with plenty of distance to react to trail obstacles with out the "tunnel vision" you get with some lights, the boost beam is pretty insane, lighting up the woods like daylight and i'll be honest was a bit too much and took away some of the thrill and psuedo danger of night riding, nice to have but i'd say 95% of the time you just wouldn't use it
i was out around 2.5hrs playing with all the levels and the cutie was on for the whole time and showed no sign of losing power (i'm sure Troutie can give you the burn times
edit:full will go for about 2 hours
medium will go for about 8 hours
low will go for 33 hours
to conclude, it's an awesome light, it'll tackle any offroad riding with ease with plenty of battery life for a decent length ride in the dark and if you were just usung it to commute it would ensure you were seen by other road users and give you plenty of spread to pic up kerbs and verges on unlit roads, my only minuse is the size of the battery but as this might not be the battery that comes with the light as standard it's a minor quibble.
oh and one more thing, this rabbit was alive before it got caught in the Cutie's beam...and when we checked it, it was cooked! 
cutie killed a bunny by rOcKeTdOgUk, on Flickr
