Simpler cluster management both with RAC and DataGuard. Easier tuning, optimization with improved functionality in ADDM, Segment advisor, Automatic backup (now with full tape support (no need for that $10k Legato license!)).
The new query language. Now you can not just store XML/XSLT files in your database you can even query XML data (and normal "flat" data as well for course) in the next xquery language.
Microsoft CLR (common language runtime)
Now honest I'm not sure if this is really a good thing, but anyway, you can now have stored procedures written in VB and C#. My worry is that this will open the doors to many junior programmers to destroy what I love about Oracle ("It just works!"). I'm sure that Oracle will attract a few new customers with this addition though.
How many times hasn't a DBA been in the position to think "Ok, lets do a backup before we start this huge data manipulation operation"? Now you can do that even without messing backups, just create a database restore point and if you encounter problems you just "flashback" the database to your restore point.
Clusterware HA API
This I've been waiting for, now you can write your applications to natively support full cluster failover and recoveries. Restart and application at node failover or balance your application servers even before the Oracle client layer.
Transparent Data Encryption
Encrypt data on-the-fly, create a table with encrypted columns. Even the DBA can't access the data without the key used when inserting the data.
Really something for everyone, I can see that the improved CLR and PHP support will probably sell a few SE One licenses and the terrific cluster and manageability enhancements will give EE a boost as well.
OTN has the full story. I can recommend the podcast with Ken Jacobs.
Check if any (l)users have stored data objects in the wrong tablespace. I keep finding indexes in the data tablespaces all the time. May be worth to check every two months or so if you have optimized your storage and keep indexes different spindles.