I ran across this very useful performance counter today: SQLServer:Deprecated Features. This shows you how often SQL Server encountered listed deprecated features since the latest start.
In my SQL 2008 environment I see such item as "String literals as column aliases" or "sp_change_users_login." Some of these features are self-explanatory. For example, I can deduct from "Table hint without WITH" what I need to use the keyword "WITH" for table hints to correct this for a future version of SQL Server when skipping WITH will not be allowed.
For some others it's not so obvious or I need to find out another option. In those cases I can look at Microsoft's page that describes all the deprecated features in detail giving alternatives: http://technet.microsoft.com/en-us/library/bb510662.aspx. On this article, for instance, I find out that instead of DBCC DBREINDEX I need to use the REBUILD option of ALTER INDEX.
If you have a lot of legacy code in your application (and who doesn't?) be sure to take a look at this counter by running the following SQL statement: SELECT * FROM sys.dm_os_performance_counters where object_name = 'SQLServer:Deprecated Features'