[I posted this on the Slate fray, and a reply noted that the real issue is the lack of congressional checks. This sort of misses the point: it is not either/or. You address what one branch can do and what others should do when it fails to do it. Both are necessary. One hopes a good executive will come into power at some point. Spelling out the limits of his/her power is therefore useful.]
Walter Dellinger had an article on them recently and said the problem with President Bush was the way he used them, including the breadth, vagueness, overuse, and loathing to submit things to judicial interpretation. They are not per se wrong.*
I agree. For instance, executive agencies interpret statutes all the time, providing rules and regulations to help the interpretation. They need to .. they "execute" the law. A legitimate means to better clarify the process, including from conception, is not really a bad thing. And, especially regarding omnibus legislation, the President need not veto legislation if only a small subset is unconstitutional. Or, at least that has been the practice.
[Doing so in such a way that it twists the words of the legislature or refusing to supply information spelling out what you did is quite different.]
Dellinger et. al. provide extended remarks including links to his previous statements on the matter here.
I know this is a bit of shade of gray -- he isn't totally wrong, but shades of gray is a major concern of my side of the debate, so it should not be a surprise. Perhaps, the statements will be used by those who will so abuse them that the special care required is so lacking that they are too dangerous.
But, such is the nature of governmental power. The fact we have reached such a point is ominous.
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* Some suggest signing statements can in part be used as a sort of "executive history" to obtain the understanding of those who signed a bill into law. The courts have not as of yet found this too useful but it might be of some limited value. The linked piece touches upon this matter for those interested.
I'm not totally against the idea though think legislative history is the best approach. Anyway, the courts do give broad discretion to agency interpretation unless certain specific reasons (such as First Amendment concerns) might guard against it. This suggests the importance of avoiding overly vague laws.
And, many Bush signing statements seem geared to executive officials, who the administration does not want the courts to interfere with (and often whom they won't affect anyway).