Any SQL issues going from 10g to 11g

We are getting ready to move our 10g systems to 11g.  When we migrated from 9i to 10g some of the "bad habits" that our programmers had gotten away with in 9i (not putting order by statements in reports that have group by for example) stood out like a sore thumb. 

Does anyone know of anything that works as a default in 10g that 11g handles differently?  I am just trying to be proactive and fix problems before we go to 11g.

Thanks for your responses.