I bought the Apollo Quad, and am generally very impressed with it. It's an excellent product -- but not great yet. What it does is very powerful, and it could be a complete home run if it did more.
-Low latency tracking
-Metering & aesthetics
-Rudimentary signal routing
-Runs only UAD plugins
-Requires 32-bit bridge in 64-bit DAW (still!)
The more serious you are about your ITB performance, the more the Apollo is a no-brainer. The core virtues of the box (no-latency tracking with plugs, superb audio quality) are worth it if you care enough about those things to spend $$$$. Thunderbolt will be huge. 3rd-party hosting would be a dream. Omnisphere via 88RS & A800, with no latency? GOOD GOD PLEASE.