Rick Perlstein has the goods on what a shoddy, faux-think tank Heritage is. But sad as it is that they write fundraising letters as if they were city council candidates in Texas, it's the tip of the iceberg: It's not just that they don't respect research, it's that they often don't respect their own research, which makes it hard for anyone else to trust the findings. I've heard stories of their people publicly decrying and denying their own research because it proves ideologically inconvenient (I'll try to get permission to tell some tomorrow).
As a general guide, Heritage is generally considered the most hackish of the major conservative think tanks. AEI is quite a bit better, with serious researchers scattered among the more occasional ideologues (though they still have their share of shameful moments). And Cato, which is libertarian rather than conservative, is usually quite above the board.
