I was wondering the same thing. Our startup currently uses it when doing research on data sets, but it's a db I don't hear about very often when talking about startups. I'm assuming a big factor is price.
I use to work with Oracle daily (previous job) and now I use MySQL mostly with some Postgres and SQLServer at times (lots of client work).
I would say all these databases are worthwhile as long as the DBA is competent. Given that, unless you have a reason to choose Oracle (e.g. familiarity, integration with other applications, a specific Oracle only feature, contractual obligation), I see no reason to choose Oracle. Many companies choose Oracle because Oracle built a solid database/brand early on while catering to big businesses. MySQL and Postgres made great progress in the past decade make them valid alternatives.
The licensing is really an issue, especially when you get into the higher-end. They don't charge per computer, they charge per CPU. So you'll have to pay 4x as much in a dual CPU system (I'm not sure if they have a similar licensing structure for dual-core or quad-core systems)