Cisco has been saying that they are going to drop CatOS for years...yet is still exists. I did notice that there is a new product line, the NX series switches that have a new nx os. If you add in the PIX os that is 4 OSes that Cisco has.... at least.

If you have a large number of routers and then Cat OS switches, I personally have found it easier as far as management to have as many devices as possible on the same OS. In my organization, I have routers, switches, routing switches and AP's all using IOS and then my PIX running PIX OS.

There is like a 20 step doc in how to convert from Cat OS to IOS on cisco.com