Although I’ve never used the IE7 script before, one other thing that may be worth considering is that even if you use conditional comments for IE6, you’re still not going to be able to have access to all the extra CSS2 goodness (e.g. attribute selectors) without javascript. So if you like to use that in your projects on a regular basis, it may be another tipping point in favour of js over conditional comments.
Although I’ve never used the IE7 script before, one other thing that may be worth considering is that even if you use conditional comments for IE6, you’re still not going to be able to have access to all the extra CSS2 goodness (e.g. attribute selectors) without javascript. So if you like to use that in your projects on a regular basis, it may be another tipping point in favour of js over conditional comments.