I've done a lot of defending of some blue dogs. Some people have voiced different opinions :-).
Just to show that I am not in favor of all conservative Democrats, below the fold I list some people who should be primaried, and why.
Senator State Ranking
(1 = liberal Obama pct Seat up
102 = most cons.
Carper DE 48 62 2012
Lieberman CT 34.5 61 2012
Mikulski MD 33 62 2010
Casey PA 36 54 2012
Cantwell WA 25 57 2012
Murray WA 25 57 2010
Wyden OR 25 57 2010
Nelson FL 34.5 51 2012
ranking data there are 102 because of replacements mid-term
The above list is in order of mis-fit with the state.
Now, let's look at the popularity of these people.
Carper was elected to the Senate in 2000, running against incumbent William Roth, and won 56% to 44%. In the 2006 general, he won easily. There was no primary in either year. In March, 2009, 57% approve, 26% disapprove.
Lieberman - oy vey! Back in November 2008, he was at 35% favorable, 63% unfavorable. Lamont would win 59-34.
Mikulski. I could find no polls about her, but she's been in the senate since 1986. In 2004, she won a primary with 90%. She might retire, she was born in 1936, so in 2010 she will be 74, not that old for the Senate, but she's had a long career, she was in the House starting in 1976.
Casey. In February, he got 54% approval, 23% disapproval. In the 2006 primary, he beat two more liberal candidates, who may have split that vote, but he did get a huge 85%.
Cantwell. Back in July, 2008, she was only at 50% approval. In 2006, she got 91% in the primary.
Murray. Also in July, 2008, she was at 56% approval. In 2004 she got 92% in a primary.
Wyden. I could not find anything on his popularity. There was no primary in 2004.
Nelson. By far the least bad fit of this list. There was no primary in 2006. In February, his approval was at 48% approve, 22% disapprove
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I leave it to the daily Kos readership with local knowledge to add to this.,