What do you mean by "default rootfs"? Is it the one in January 2007?
If so, then you have to use the Angtrom tslib, which is debianized and packaged in yonggun's page, and is also available in my previous after installation tarball and the configured rootfs tarball.
For Angstrom kernels, you have to do two things to set up touchscreen:
Step 1: Specify the correct device
edit ~/.profile and make sure you have these two lines:
export TSLIB_TSDEVICE="/dev/input/event1"
export TSLIB_CONFFILE="/etc/ts.conf"
Step 2: Edit /etc/ts.conf
Comment out the line "module_raw corgi" (as djl0 says).
Then run ts_calibrate again.
AFAIK, with the yonggun kernels the differences are:
-- the device is /dev/input/
ts0-- the "module_raw corgi" line is NOT commented in /etc/ts.conf
Hope this helps.