On the current project I am working on, I have been introduced to Oracle. I have never come across it before - usually use SQL Server in various guises.
The installation process was a little harder than SQL Server, as the server we had been supplied had Java locked down on it. Basically the installer wouldn't run as it's a Java app. A boffin managed to find a work around and got it installed.
I guess being multi platform is a good thing - but to me the Java interface looks dated and is a lot slower than a native Windows app. The actual interface itself is a little clunky also. I don't believe it's as intuitive as SQL Server 2005 for example, although I am a lot more familiar with SQL Server.
Once you get up and running though, it's not too dissimilar than SQL Server. I did read an article talking about update-read locking and how Oracle allows users to read data on pending updates. I guess the thought process is that the update may never happen so why lock a process from reading. I guess it's a good feature to have that option. SQL Server just locks the read in that scenario.
From a front-end point of view the two are the same - I use the new .NET 2.0 data factory pattern (System.Data.Common) when connecting to databases anyway, so from that point of view nothing in my code is different for use with Oracle or SQL Server (or mySQL or any other db for that matter).
Anyway, so far no real issues with Oracle. I much prefer SQL Server, but I guess that is more to do with familiarity than any negative aspects of Oracle.