Coldfusion version compatibility

Take a look at the release notes for CF8 and CF9 and find the new functions.

Your client may have made custom functions with the same name. Also take a

look for blog post about the local variable scope. It may cause code issues

if your client made its own local variable. Nothing to hard to fix, some

quick searches of the code should identify them. Often a search/replace of

function names is all you need.

Nothing that should be insurmountable.  But there are a couple of deprecated tags.  A few more that might behave somewhat differently.

In general ColdFusion has been pretty darn good (some might say too good in some cases) at backwards compatibility.  But that still doesn't mean that one would not test, test and test some more in a labratory or development envirnment BEFORE any offical migration.