[2011-06-15 12:40:03] soren@lenny:~$ gpg --list-keys 9EAAF9C5
pub   4096R/9EAAF9C5 2011-06-15
uid                  Soren Hansen <soren@linux2go.dk>
uid                  Soren Hansen <soren@openstack.org>
uid                  Soren Hansen <sh@warma.dk>
uid                  Soren Hansen <soren@ubuntu.com>
sub   4096R/DCBF5BE3 2011-06-15
sub   3072R/CE6B48BA 2011-06-15
sub   3072R/021C47D4 2011-06-15
sub   3072R/9997F71D 2011-06-15

Those three 3072 bit RSA keys are on an OpenPGP (v 2.0) card.
I generated them using the addcardkey command.

[2011-06-15 12:40:12] soren@lenny:~$ gpg --edit-key 9EAAF9C5
Secret key is available.

pub  4096R/9EAAF9C5  created: 2011-06-15  expires: never       usage: SC
                     trust: ultimate      validity: ultimate
sub  4096R/DCBF5BE3  created: 2011-06-15  expires: never       usage: E
sub  3072R/CE6B48BA  created: 2011-06-15  expires: never       usage: S
sub  3072R/021C47D4  created: 2011-06-15  expires: never       usage: E
sub  3072R/9997F71D  created: 2011-06-15  expires: never       usage: A
[ultimate] (1). Soren Hansen <soren@linux2go.dk>
[ultimate] (2)  Soren Hansen <soren@openstack.org>
[ultimate] (3)  Soren Hansen <sh@warma.dk>
[ultimate] (4)  Soren Hansen <soren@ubuntu.com>

If the OpenPGP card isn't inserted, I get this:
[2011-06-15 12:42:22] soren@lenny:~$ gpg --clearsign -u 9EAAF9C5 signing-test.txt
gpg: selecting openpgp failed: ec=6.112
gpg: signing failed: general error
gpg: signing-test.txt: clearsign failed: general error