I've been working with the BluePrint.css framework on a project. It works well.
However, like most of the CSS frameworks I've looked at, it appears geared more to a text-heavy newspaper-esque layout. It gets a bit more difficult to use when using it for building web applications that utilize a 'widget' metaphor such as SharePoint or iGoogle or the like. The key issue being that in a web app, it's often standard to create visual containers of information. This introduces a box which needs padding which ends up breaking the grid.
Another way to explain is if your container box spans 8 grid columns, you won't be able to fit 8 grid columns within it, as the container box has padding.
I've found workarounds for this but they all entail adding another layer of CSS that gets a little cumbersome. Before I continue on to the next project, I thought I'd see if anyone else has run into this issue and a) found a grid system that does accomodate this visual requirement or b) found some clever ways to accomodate this in one of the existing CSS frameworks.