We go to great lengths to ensure that Foundation works as expected on a variety of common browsers and devices. Given how forward-facing Foundation is there are some aesthetic properties which are not supported in older browsers (border radii, box shadows, etc), but the core elements are reliable across the board.
We know it can be hard to get clients to ditch support for IE8. We're hoping with the auto-update to IE10 release from Microsoft, we won't need to worry about it anymore. Until then, here's a gist with a grid that will work in IE8, just like it did in Foundation 3.Foundation IE8 Grid
We've written a comprehensive Migration Guide to help you update your code for an existing or work in progress project.