I got accustomed to OWB's memory problems in the interface since 10 years, it has never been fixed properly. The screen is frozen for minutes and nobody knows why. But since 10gR2 thinks improved and with 11gR2 you can work reasonably. But today I installed 11.2.03 patch and it's slower then ever. What can I do? I don't like ODI very much and prefer using OWB but you can see in the ODI studio a good example how a Java client interface can work as lightweight as we know it from Windows applications.
Have you tried analizing the OWBSYS schema? You can do it directly from SQL Plus or using Tools -> Optimize Repository in OWB. Oracle recomends running the optimize repository option from time to time.
the solution was surprisingly: I dropped the newly created database (UTF8) and created a new one with the WE8MSWIN1252 character set. And now it works perfectly!
I didn't know that UTF8 is just for the "Big Boys". I tried it since my customers insist on UTF8. But they have some Unix with 64 Bit. That's too much for my poor Win7.