We’ve been with Vista since middle/end of last year. Despite our road testing (which went well) and my own initial experiences of Vista (not that bad) we are seeing performance issues esp. with bootup and crunching large files.
So yesterday we took the decision to offer our laptop users the option of downgrading to XP if they would prefer the performance gain. Especially given the recent coverage here (via Crunchgear). Desktops still seem to be working fine on Vista since they are more powerful machines. But even the maxed out laptops we are using can be pretty slow with Vista.