I've downloaded the evaluation edition of SQL Developer 1.1.
It's great that I don't have to set my NLS_DATE_FORMAT everytime I connect.
BUT, one of the changes to the Explain Plan is that some operations are being coloured red, including Cartesian Joins and Full Table Scans.
1.0 was fine. Nice, simple, black and white.
Using Explain Plan, Oracle tells us the optimal plan that the Optimizer came up with for the query we gave it. It doesn't tell us the second best plan, and keep the best hidden away. It doesn't tell us the plans it rejected. It doesn't tell us "But you'd do better with a TO_CHAR on this to make us of an index" or "The stats indicate you don't have any nulls in this column, but it does allow nulls so I'm having to avoid this index". If you asked Oracle to join a table to itself on the primary key, the Explain Plan still wouldn't say "Are you just plain stupid ?" In short, the Explain Plan does NOT tell us what's wrong with an SQL.
10G has introduced features to make suggestions about how to improve SQLs, for example suggesting new or changed indexes. Those features are not part of the explain plan. The Explain Plan describes what the optimizer decided was the best access path, with the cardinality and costs giving a (vague) suggestion as to why it might have decided that. The 10053 event can be used to obtain very detailed trace information on why a particular plan was chosen ahead of other plans.
A developer (or DBA) can look at an Explain Plan, and (if desperate) the 10053 trace, and use their knowledge of the business, the application, the data and the requirements to see if Oracle has made any incorrect assumptions based on insufficient data.
Quite simply, you cannot look at an Explain Plan and, without any additional information, say "This plan is BAD". Worse is the concept of saying "This operation in this plan is bad". The plan is the sum of the operations. You can't just excise one and pretend that there's a magic way of doing that process for free. Even worse than that is saying "This operation is pretty much always a bad idea."
Sticking a highlighter over the Explain Plan is trying to turning the very complex process of query optimization into a childs game of follow-the-leader and it won't work.
"FULL SCANs must be bad, SQL Developer Says so."
I say NO, and I'll keep a SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY) in my snippets folder.