I'd wait for the simple reason that 7 will be supported longer and new software will be written for 7.  Vista works great for me but that is irrelevant.  It's not going to be around as long.  

Too if you get a  computer with Vista you might get an upgrade to 7 free and while that sounds good I don't think it is.  They did that with XP and Vista and it had problems.  Starting with a fresh clean install of the new 7 is better than trying to upgrade over Vista and then there may be problems getting 7 when they goof up the upgrade certificates like they did with Vista.