Limitations:

• The Selenium remote control is quite slow at driving the browser. Therefore, unless your application or your network is especially slow, the remote control/browser pair will end up being the bottleneck of your test suite.
• You can only run a limited number of concurrent tests on the same remote control before seriously impacting its stability. Practically speaking, launching more than 6 browsers on the same Selenium Remote Control is not advisable. The limitations are even more drastic for Internet Explorer.
• Your tests can target multiple Selenium Remote Controls to work around the limitation on the number of parallel tests that you can run on a single remote control. Nevertheless that does not scale very well. It can easily be done at the continuous integration build level (one for Internet Explorer, one for Firefox, one for Safari). However, allocating a Selenium Remote Control to a specific test quickly becomes a nightmare if you want to run your selenium tests in a highly parallelized fashion. Your tests also become way too aware of the Selenium Remote Control infrastructure, which makes it difficult to evolve your infrastructure transparently.