We've got an instance of SQL Server 2008 running in production and I had no idea it was a trial version - until it expired! Now I can no longer run SQL Management Studio and SQL Reporting Services will not start, but SQL Server itself (ie. the database engine) continues running and users can still access data as normal (apart from reports). My question is: how long will it continue to work? Is there a time when it will just shut down and refuse to start again?
Pretty much the next time you reboot the server, or restart the service it won't start up again.
You can upgrade from the eval to a paid for build by using the /SKUUPGRADE switch when you install the new version from the CD/DVD/ISO.
I have not used the trial but as no one else has answered I would say that this is along the lines of other MS trial products - you can continue to use it until the service/program is restarted.
2008 trial to standard is a supported upgrade path, so unless there are features from enterprise you are using, I would upgrade if possible.