Upstream systemtap-20080927 has been released, http://sources.redhat.com/systemtap/ftp/snapshots/systemtap-20080927.tar.bz2 The systemtap-0.7.ebuild has already been unable to run on linux-2.6.27-rc5 kernel, I just copied systemtap-0.7.1_pre20080830.ebuild to systemtap-0.7.1_pre20080927.ebuild in a local overlay, This systemtap-0.7.1_pre20080927.ebuild works well now, I have tested.
I just commited 0.7.1_pre20081004 to the tree.