Unless there are features that you need in 8.0.90 I would stay on the .80 builds and look to move to .90 when it is more mature. And as a general rule only upgrade when necessary i.e. there are features and/or fixes that you need in a later release that the one you are already using.
If you are using SmartZone 5.1.1 to manage your switches you should move to the latest .90 version as this release allows SZ based switch configuration from the GUI.
Note that 8.0.90 will be the next Target Path release, hopefully later this year.