Selenium Grid allows you to run Selenium tests in parallel, cutting down the time required for running acceptance tests to a fraction of the total time it currently takes. Run them all on a single machine (we've run up to 15 parallel processes on a laptop!) or on a server farm.

Technical Mumbo Jumbo:
Selenium Grid runs on top of Selenium Remote Control. Selenium is a test tool that allows you to write automated web application UI tests in any programming language against any HTTP website using any mainstream JavaScript-enabled browser.