PowerShell team has just posted the latest pre-release drop of the upcoming version 2 – and they did in on track with the timeline they announced back in November.
The current version of PowerGUI (1.5.3) which you can download from PowerGUI.org is in general compatible with CTP3 but does have a few issues. For example, the editor works fine and you can get syntax highlight and intellisense for new cmdlets, but step-by-step debugging might leave awkward yellow marking on previous steps.
These issues are obviously fully fixed in the upcoming 1.6 release which is coming out literally in a matter of days now. Stay tuned.