If you have to use PostgreSQL instead of Oracle or DB2, what feature would you miss the most? I'm specially interested in features which are important for high availability OLTP applications. Thanks!
Edit: I'm looking more into technical limitations. Let's assume you have the same level of expertise in PostgreSQL, Oracle and DB2.
Management backing / trust / support
and I mean your/my management, not IBM/Oracle's ..
We all tend to trust more what we know (a very successfull survival strategy). Management types more often encounter DB2/Oracle than a free DB at the functions they attend (Telco with the company I work for). Naturally they will lean towards the better known products.
I know this has changed much in recent years as MySql, PostgreSQL and other more open/less costly products get mentioned in (management/business) news articles and used successfully in critcal systems...
Update: I've set the community wiki flag since you now say you are looking for technical information, which my answer definitely isn't.
Application Express for development
The Oracle Wait interface for performance tuning (though I would be happy to be told about Postgres equivalents).
Oracle RAC for scaling to multiple servers using the same dataset.
@Gary Regarding RAC, Postgres now supports WAL-log shipping since version 8.3, if i recall correctly. This isn't quite as good as a shared cache system but it allows real-time replication for scaling as well as redundancy.
I feel self-tuning is really where PostgreSQL has fallen far behind. You can achieve very decent performance even on very large datasets in PostgreSQL but it requires very tedious tuning work in terms of server configuration and indexing to reach it, whereas Oracle and MS-SQL server tend to do a lot of that work automatically.