When it comes to the movement of data around the enterprise, the focus is usually on the hardware systems within the infrastructure (routers, switches, HBAs) or the protocols they use.
But DataDirect's Mike Johnson makes a good argument in this article on SOA World that when it comes to database communication, the bottleneck has moved to the middleware layer, particularly the data connectivity software stack. What's more, he says the increased use of server virtualization can exacerbate the problem because most drivers are stuck in a per-virtual mentality.
The simple fact is that all data connectivity solutions are not created equal. There are significant differences in the way drivers like ODBC and JDBC operate. But since they are usually included as default components within commercial database offerings, they are rarely given any consideration.
The drawback to this state of affairs is that if the connection layer is loaded up with numerous tools like libraries and disk caching, they may end up overusing network resources. He offers up a number of ways that third-party drives can be fine-tuned to improve network performance, so it's probably worth a read -- even if you're not fully up to date on the minutia of middleware connectivity solutions.