(now to the list)
On Kubuntu 9.04 (amd64):
On Ubuntu 8.10:
$ pkg-config --libs dbus-1
-L//lib -ldbus-1
This leads to
configure:13190: checking for dbus_connection_close in -ldbus-1
configure:13225: gcc -m32 -o conftest -g -O2
-DDBUS_API_SUBJECT_TO_CHANGE -I/usr/include/hal
-I/usr/include/dbus-1.0 -I/usr/lib/dbus-1.0/include conftest.c
-ldbus-1 -L//lib -lhal -ldbus-1 >&5
/usr/bin/ld: //lib/libdbus-1.so: incompatible target
configure:13253: result: no
Also affects sane.
Haven't checked Jaunty yet to see if it's still busted.
We may need to postprocess pkg-config's output to add the missing 32
in some cases. Not sure if it's worth it.