Oracle bought GoldenGate and has been pushing it lately as opposed to its Oracle Streams product that debuted as a built-in feature of Oracle 9. GoldenGate captures DML events from the transaction log, writes them to "trail files," then pumps them across even a WAN.
You can configure the database in "multimaster" setups where both instances allow writes. In this event, you can have write conflicts. Write conflicts have to be resolved and GoldenGate has ways to do that, but this may require work on your part. Multimaster can help read performance from a scalability standpoint but does not help at all with write performance. The same number of writes (systemwide) will take place on each node, resulting in no greater performance than before.
Implementing GoldenGate requires that you create mapping files. This will feel a lot like a system integration project, and depending on the size and complexity of the database, it may have the scope and risk of one. A key advantage to GoldenGate is that it allows you to mix and match Oracle versions.
You need to do due diligence in performance testing and ensure this product meets your performance goals. Check out Oracle's diagram of how GoldenGate works and you'll ask: Wow, how long will it take to do this on my database and network infrastructure?
A number of other third-party products do transaction replication -- indeed, Oracle has another product called Data Guard, which can do transaction replication in single-master mode. However, Oracle seems to be struggling to explain why it has both Data Guard and GoldenGate. The simpler explanation may be that GoldenGate will take you longer to implement.
The primary "data" way to scale in Oracle comes down to partitioning. Here's Oracle's definition:
Partitioning allows a table, index, or index-organized table to be subdivided into smaller pieces, where each piece of such a database object is called a partition. Each partition has its own name, and may optionally have its own storage characteristics.
Now here's 10gen's explanation of sharding in MongoDB:
If you have RAC for the instance balancing and partitioning for the data balancing, then you have much of what sharding provides while still in your familiar Oracle database, right? Almost. There's more involved in setting up and maintaining partitioning in Oracle. There are multiple schemes for how to partition.