just tried it and got the following error:

rake pkg:deb
(in /home/ohad/git/foreman)
This package has a Debian revision number but there does not seem to be
an appropriate original tar file or .orig directory in the parent directory;
(expected one of foreman_0.1.5.orig.tar.gz, foreman_0.1.5.orig.tar.bz2,
foreman_0.1.5.orig.tar.lzma or foreman.orig)
continue anyway? (y/n) y
 dpkg-buildpackage -rfakeroot -D -us -uc
dpkg-buildpackage: set CFLAGS to default value: -g -O2
dpkg-buildpackage: set CPPFLAGS to default value: 
dpkg-buildpackage: set LDFLAGS to default value: -Wl,-Bsymbolic-functions
dpkg-buildpackage: set FFLAGS to default value: -g -O2
dpkg-buildpackage: set CXXFLAGS to default value: -g -O2
dpkg-buildpackage: source package foreman
dpkg-buildpackage: source version 0.1.5-2
dpkg-buildpackage: source changed by Jochen Schalanda <jochen@schalanda.name>
dpkg-buildpackage: host architecture i386
dpkg-checkbuilddeps: Unmet build dependencies: cdbs
dpkg-buildpackage: warning: Build dependencies/conflicts unsatisfied; aborting.
dpkg-buildpackage: warning: (Use -d flag to override.)
debuild: fatal error at line 1340:
dpkg-buildpackage -rfakeroot -D -us -uc failed
Error while building the DEB package with `debuild`.

am I missing something?

dpkg-checkbuilddeps: Unmet build dependencies: cdbs
dpkg-buildpackage: warning: Build dependencies/conflicts unsatisfied; aborting.

You should install the package cdbs as it's needed for building the foreman .DEB package.

I'll have a look at how to automate this in the Rakefile when I find some time.