Few Democrats(*) endorse Bush's doctrine of [link|http://www.cfr.org/publication.html?id=5251|"preemption"] - saying we'll go to war before a threat is imminent. Few Democrats endorse Bush's doctrine of the [link|http://writ.news.findlaw.com/commentary/20060109_bergen.html|"unitary executive"] and its corrollaries - e.g. The President can do almost anything under his [link|http://caselaw.lp.findlaw.com/data/constitution/article02/|Article II] powers in a time of war, no matter what other laws are on the books. Few Democrats think that every tax increase is bad no matter what the circumstances, and every tax cut is good no matter what the circumstances. Democrats are far more likely to favor greatly increased government participation in providing heath insurance to a larger slice of the population, and reigning in excesses in pharmaceuticals, finance, mergers, tax evasion, etc., etc.
Few Democrats accept Bush's "Culture of Life" with all its ramifications (abortion outlawed, stem-cell research greatly restricted, state and federal politicians jumping into [link|http://en.wikipedia.org/wiki/Terri_Schiavo|end of life decisions], opposition to [link|http://egov.oregon.gov/DHS/ph/pas/|Death with Dignity] acts, etc., etc.).
Yes, there are far fewer differences than there were in, say, the early 1970s on issues like labor law, "free trade", bailing out corporations, etc. I think that's unfortunate, because the battle of ideas makes our country stronger. If everyone agrees on too many issues, we're more likely to be blind-sided by technological change or a crisis.
My $0.02, FWIW.
[edit:] Completed a thought in the second paragraph.
Cheers,
Scott.