Martin are you using the new or old s.surf.tps?
The new one by now (s.surf.2d from /grass/incoming/interp_lib_new.shar)
raster files with all zeroes can occur if your data are floats
0-1 and integers make them all zeroes. It is possible that your
new data set needs completely different parameters than what
you were using before and that's why you are getting the visible segments.
(for visible segments increase npmin - with old s.surf.tps you
can go up to about 350, with new one, I have used npmin for some
very bad data as large as 600 with good results).
Well, I'm still at the same point - nothing but zeroes.
My site file looks like this:
619946.25|4176606.87|#58000
619943.75|4176615.62|#58000
619929.37|4176638.12|#58000
619904.37|4176671.87|#58000
619893.75|4176681.87|#58000
619893.75|4176709.37|#58000
619893.75|4176771.87|#58000
(that's file sh2, heights in cm)
The region is as follows:
north: 4179364.07936508
south: 4176563.19047619
east: 621668.20404722
west: 619370.06576728
nsres: 20.00634921
ewres: 19.98381113
rows: 140
cols: 115
and the history of the elevation file looks like this:
Thu Aug 11 17:28:05 1994
e2
PERMANENT
ma
raster
site file sh2
generated by s.surf.2d
tension=40.000000, smoothing=0.100000
dnorm=15705.616146, dmin=9.991906, zmult=0.010000
segmax=40, npmin=200, errtotal=0.000000
zmin_data=0.000000, zmax_data=0.000000
zmin_int=0.000000, zmax_int=0.000000
You'll notice that zmin_data and zmax_data are zero.
I've run the same thing through the old s.surf.tps. That gives me a
file without obvious segmentation, but with weird values (not a lot of
connection to the site values). The history of this file is:
(I've changed the resolution to 50m from 20m above)
Thu Aug 11 17:55:33 1994
e3
PERMANENT
ma
raster
site file sh2
generated by s.surf.tps
tension=40.000000, smoothing=0.000000
dnorm=1002.899713, dmin=24.979764, zmult=0.010000
segmax=40, npmin=150, errtotal=0.000000
zmin_data=0.000000, zmax_data=860.000000
zmin_int=-3532.220660, zmax_int=6055.869155
Increasing the tension to 80 yields:
Thu Aug 11 18:27:18 1994
e4
PERMANENT
ma
raster
site file sh2
generated by s.surf.tps
tension=80.000000, smoothing=0.000000
dnorm=1002.899713, dmin=24.979764, zmult=0.010000
segmax=40, npmin=150, errtotal=0.000000
zmin_data=0.000000, zmax_data=860.000000
zmin_int=-763.460313, zmax_int=1086.388382
The actual values in the site file range from 52000 to 92000.
I guess the high values are cut of by dmin, but there's definitely
no value lower than 52000 (or 520 with zmult) in the site file.
(sh2 contains 4672 points of which 3714 are ignored due to dmin).
If you cannot get reasonable results from your data set it would be better
if you send us the data and region information so that we can find
out where the problem is. You can try to run s.surf.tps on your
old data set or any other data you have to see whether your installation
of program works OK.
I can send you any information you need, but as yet I can't seem
to get any useful output from s.surf.tps and friends 
Martin