I can understand some cases of strategic voting. Voting for the less bad candidate because the good candidate doesn't have a chance of winning is probably reasonable (sure, your vote probably won't matter, but I hope Florida voters who voted for Nader in 2000 have spent the last several years hating themselves).
However, I disapprove of strategically supporting the "electable" candidate in primaries. If it's clear to you who the best candidate is, support them, and do your best to explain to everyone you know and publicize as widely as you can why they're the best. Then may the best candidate win the primaries. If, in the primaries, people support the candidate they're enthusiastic about, then in the general election, you'll have a candidate with a lot of enthusiastic supports to evangelize for their cause, and to volunteer and raise money of course. If they hold their noses and support the "electable" candidate, then they'll get a candidate with a bunch of lukewarm supporters, who can't explain why they're supporting the candidate except with a lame story about how he's at least not as bad as the other guy.
Thus, for example, I think the Democrats would have done a lot better with Dean in 2004, because I think too much of Kerry's support was of this useless, lukewarm kind. Actually, based on what I now know about Dean and Kerry, I now have some inclination to think Kerry might have made a better president than Dean would have (back when I was supporting Dean, I didn't know enough about Kerry), but his lukewarm supporters didn't seem to bother to learn enough about him to know how to sell him with enthusiasm. I also think that if Gore, Dean, and/or Kerry want to run again in 2008, more power to them. If any of them can get more enthusiastic supporters this time around, as they'll need to in order to get the primary victory, then I'm sure that candidate will have a solid shot at winning. Certainly any of the three would have my enthusiastic support (all of them have good ideas on health care, and they all have other notable strengths as wellm such as Gore's record on the environment, Dean's on fiscal responsibility, and Kerry's on corruption).
Similarly, nobody should support Hillary Clinton because they think she's electable, or oppose her because they think she's not. If you think there are reasons she'd make a better president than any of the others in the primary, support her for that reason, if not, don't.