Replication and compatability are very different things though. There are equivalent applications on the Mac of course, but these applications must not only be able to convert from Visio or Project format, but save in that format as well, because in most companies work is collaborative. Whilst there are no open formats, this is critical. If the equivalent software cannot work on documents produced by their coworkers using Visio or Project, and importantly vice versa, it's not a viable option. Corporate policy doesn't allow this to happen, regardless of whether someone is willing to expend all the extra time of dual-booting or virtualisation: (in general) corporate IT departments are not going to want to support it.