I've been testing the latest version of SQL Server (SQL Server 2012) with Forecaster. I've been using Forecaster 7 SP3 with CU#5 (aka, the latest version that is readily available).
To date, there have been no problems with Forecaster itself. No unexpected errors, no connectivity issues, no functionality failures. There have been occasional instances where the Database Wizard did not function properly, so if you anticipate needing to create new Forecaster databases you may want to try this out in a test environment before migrating to production (workaround if you encounter this: if you still have a SQL 2008 server you can create the database there, back it up and restore it to the 2012 server).
Note that it will still require that you follow the instructions for connecting to SQL Server 2008 databases (due to the Database Wizard and ExpressLink). Details of that are here:
Similarly, you will need to manually apply the 64-bit versions of these items if you are running Forecaster on a 64-bit machine. Details for this are here:
Finally, if you are running Forecaster 7 SP5, you need to follow the instructions in THIS post:
Bottom line: Forecaster 7 appears to work absolutely fine with SQL Server 2012. This is good news! I will update this post if new information comes to light about it.