If you want to try our newest engine, Presto 2.4, you can download the Opera Mobile 10 beta for S60. This beta is the first public version with Presto 2.4. There are some limitations, though, as listed in the Opera Mobile 10 beta developer's introduction on Dev.Opera.
I don't have any updates on Carakan or Vega, but our core team is continuing work on Presto 2.4, and of course on versions beyond 2.4. There are a lot of goodies on the way for versions after 2.4, and hopefully we will be able to get future versions out much sooner.
So what happened to Presto 2.3? Well, it's actually out there in some products, such as the Linux SDK. For those of you who need more information on Presto 2.3 or if you are just curious, our documentation team just published a document detailing the Web specifications supported in Opera Presto 2.3.