On one hand, I think it’s a good thing that there are many Republicans willing to take a stand for a secular, rather than religious, approach to policy.
On the other hand, I oppose federal funding for all non-defense research. I think that promising research is likely to get private funding (as we have seen with embryonic stem cell research itself). So, I actually don’t approve of this change in policy for fiscal and moral reasons (protecting property, not embryos).
Symbolically, though, I think it would be a shame for Bush to use his first veto for this cause, rather than something more worthwhile (like the bloated Highway Bill, for example).