WE jsut did an upgrade from V2R3 to V2R5 and there were minor problems. Run the reserevd word scriptson yoru system to check for V2R5 reserved words that you may be using in yoru current system. This one will save you some heart-ache later.
Another issue we came across is "update by multiple rows error". This one I found interesting. I'm not sure how Teradata used to handle updates by multiple rows, but it is pretty specific now. (I can post an example of what we ran across if you'd like.)
The only other issues we ran into were upgrading the utilities (ODBC, mainly), but seeing as you are already at V2R4, you shouldn't see as many problems in this area as we did.