So you're asking about the downside of the Cloud?
The primary downside is that you never stop paying your monthly fee.
To keep using the software beyond CS6 into CS7 and CS8 and onwards you are forever paying the monthly fee. That stops some people dead in their tracks because they refuse to subscribe to software on principle. Others embrace it based on what they'd normally pay to upgrade over several years anyway.
Its value to you is really up to you to determine. If you think it's a winner, then go for it.
Bear in mind that when you stop paying, you lose all access to the software and your ability to edit your existing files (unless you own an earlier version).
You can then either re-join the Cloud or buy the full (perpetual license) version outright again if it's still available.
Other than that the Cloud offers what it says on the box: full access to all Master Collection apps plus other Adobe services such as web hosting.
