When performing OLTP, if the number of data cubes we generated are too much and some processes (rollup/slide down the cubes) are going on, the system seems cannot handle it gracefully. It just hangs!!!
Based on what I've seen, an increasing number of shops are using 10gAS. I don't have any numbers handy but that's the general impression I'm getting. I've worked on the product since it was iAS (and even OAS) and I'll say the product has changed quite a bit even though it is still Apache based. I really didn't care for 9iAS V2 (9.0.2) as I thought it was buggy. That was the first release where they based the product on OC4J. However the 9.0.4 release (aka 10gAS) is much easier to work with (more stable too) and I'd recommend people go to that version if possible.
Author "Oracle Application Server 10g: J2EE Deployment and Administration"