Started working on Macs recently and got to know that there's no Visio on Mac :-(. Visio is my favorite tool for all things drawn - UML diagrams, architecture diagrams, everything. The flexibility and the breath of what's possible in Visio is enormous. I stumbled for sometime to realize a block diagram in Skitch but then finally gave up. OmniGraffle is a good alternative. Still a learning curve but very close to Visio.
