MS hasn't paid much attention to Visio of late but they have added some features that are handy for certain professions.<font face="Verdana, Arial" size="2">Too bad Ms got a hold of it and chopped it into pieces. </font>
I've used it for PFDs and P&IDs for fairly simple chemical processes and it does a pretty good job at that. Being able to simply generate one's own templates can be a big plus too.
It's also handy for laying out a shop, though there never seems to be as much room as measuring would suggest once one gets into work flow.