I develop a complex WCF/SOA enterprise application that runs on Oracle as data tier. Oracle is our company standard and there is almost no chance in getting that changed. There are other non-.net applications on top of that DB. From a developer's perspective Oracle and .Net doesn't mix easily if you want to use latest .Net data access technology like LINQ ,Entity Framework, RIA services etc. Oracle has just now announced that it will support EF with first beta coming out only later this year. We hand code our DAL using ODP.Net and StoredProcedures and that feels tedious at this day and age.
I also don't like somethings about Oracle like a 32 character limit on table/SP names, names are all upper case by default. Also Oracle queries can sometimes require hints that only Oracle specialists know. Profiling is hard when compared to SQL Server profiler.
But from a performance point of view Oracle is top notch. In the hand of a skillful DBA it is highly customizable for performance and I would strongly advice to have a Oracle specialist in the dev team (separate from production DBAs). We never had any deadlocking issue that I keep on hearing on SQL Server and Oracle works fine with Cursors unlike SQL server.
As for install/support/backup the Dev team is not involved, we have DBAs, SAN storage engineers etc. to look after those infrastructural area. SO I can't say much.
Overall I would say that if you don't have a pre-existing dependency on Oracle choose SQL Server for .Net development.