As Gary stated above, I have the SD1m. I started with the 18-250mm zoom but now have several lenses. I started with the DPxMs but I wanted other focal lengths and faster lenses.
I also wanted to go wider so I bought the Sigma 10-20mm f/3.5.
In my view, fast lenses are a must with SD1m given the inability of the camera to do well in low light (unless you convert the files in SP5 to black and white).
I continue to be amazed at the resolution of the Foveon sensors - just spectacular.
Posts by Gary and Keith on this forum encouraged me to take the plunge. I now consider other sensors to be inferior (although I still like the Fuji x-trans sensor).
You may have noticed the the SD1m price has gone down again recently.
Most of the lenses I have bought are full frame Sigma lenses so I will be ready if Sigma decides to go full frame with this camera.
After using a more traditional DSLR (such as the Canon 5D mark ii), you have to be willing to slow down with the SD1m. Buffering takes time. The viewfinder could be larger but it is ok.
Sigma primes are great, especially the Sigma 35mm f/1.4. I also like the 85 and 105mm.
The mirror slap is minimal on this camera - very well designed.
So take the plunge - especially at current prices.