You can't mix-n-match software releases, especially when there have been significant changes, as between PG 8.3.0 (for which ArcSDE 9.3 was certified) and PG 9.1 (which might not even be supported by ArcSDE 10.1). Certification testing is difficult and time-consuming, so only the version that was current during ArcGIS development is "fully supported". Minor releases are usually safe with most databases (even though they are not tested, they are assumed to work), but PostgreSQL has been more willing to introduce significant incompatibilities at even minor releases (as when the time datatype changed between 8.3.0 and 8.3.4), which makes straying from the System Requirements certification list riskier. Vince's First Law of Compatibility: For optimal stability, the application software should have been released after the server software, which should have been released after the operating system (tOS < tRDBMS < tGIS). Unfortunately, the disparity between release frequency of PostgreSQL and ArcGIS makes it difficult to use a recent PG with ArcSDE -- by the time an ArcGIS beta becomes a release, the "current" PG build is often incompatible. I had been a big fan of PG, but I no longer have the time to keep upgrading; I can't imagine how large production shops would deal with this issue. - V
