The two chair version, has a custom snapdeck, so that the 2nd chair attaches to it (it uses a clamp, so it's easily removable). I also added the Stoker bar, witch maintains compability with the chairs...
I don't like the two chair version for small commuting rides, because the center of gravity is quite high - but for long rides, it's much more confortable for the kids.
Photo courtesy
Miguel Barroso
A nice shot of a nice Trek-based Xtracycle, featured earlier as
#69 (as well as the fork swap
here)

Fantastic picture -- original Girlonbike LHT was
#150.
My Xtracycle is used. I bought the FreeRadical from a wrench at an LBS for $125. I put it on a police auction frame. Crashed, and that frame was totaled.
Now it sits on another police auction frame. An old Nishiki with friction thumb shifters.
I keep saying I'm going to buy or build more accessories. Maybe someday. :) 
Photo courtesy
Joshua

my new set up based on a kona humu frame brooks conquest big apple lumotec iq fly Photo courtesy
Fredo.
Have been Xtracycle converted since October 2008. Haven't used a car for shopping of any sort since.
Kayak photo is immediately post-build. The Specialized Rockhopper 2005 has had a few upgrades since including a new fork and most recently a Brooks Flyer saddle.
The other photo is a few weeks ago taking lots of music kit to a gig.
Photo courtesy Tom

I found this 1986 Bridgestone MB-2 on Craigslist a couple months ago with completely original components and in very good shape.
I decided to use it for an Xtracycle build and am very happy with it. Also added a Brooks B-67 saddle and am using an Aerospoke rear wheel that I already owned. The gizmo clamped to the seat tube is an attachment for a "Springer" bicycle dog leash. I take my dogs for a run with the bike a few times a week.Photo courtesy Herb
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