Does this mean that spec changed, or was it always 34mm and the web site always wrong? I went by published specs, and it does fit. I don't have calipers to measure my seat post accurately myself.
The spec changed. The alu frame seat tube diameter was made larger and the gauge of the seat-stay and chain-stay was increased [per phone conversation with Peter Reich last month].
My Xootr (2008) seat-tube has
Ø 34.0 stamped on it. I also confirmed that by measuring it with calipers prior to purchasing the 33.9mm Thudbuster ST (which I can recommend).
Getting the correct seatpost diameter is critical for the structural integrity of the Xootr Swift aluminum frame. You don't want any play there, as a little wiggle over time can cause metal fatigue. Moreover, the stresses would be translated to the seat-stay where there happens to be a large weld; welding reduces the strength of 6061-T6 aluminum by 40% in the heat-affected-zone (aka HAZ) in the immediate vicinity of the weld.
Regards
T
P.S. BTW, the Xootr website (like other bike websites) says somewhere (IIRC) that the company reserves the right to change the spec without notice. At least I seem to recall reading that standard lingo on something associated with Xootr.