Microsoft Inspire is in Las Vegas this month. Inspire is the Microsoft Partner conference, there is a huge partner ecosystem supporting Microsoft, such as solutions like Live Tiles. This is for them to get together, network, make new connections and learn the direction Microsoft is heading.
Microsoft Ignite is for the IT Professional, which could be client, services or the vendor side. IT Professionals can see all the new technology and then when they go back to the day to day they can start to implement the new ideas or software etc which came across by chatting at the booths or going to a speaking session. Ignite is typically in Orlando.