You never know if your website is Digg Ready, until you actually hit the Digg frontpage once in a while, however a Load simulation service can help you determine, if you web server is actually ready to handle huge amount of traffic.
Load Impact simulates a situation and runs a online load testing service, which will help you determine if your site can handle a large number of users, visiting your website at the same time.
Load Impact provides users with a free version, which will simulate 50 simultaneous users hitting your web server at a single time, while offering paid alternatives where you can simulate upto 5000 concurrent users.
The load impact tests always tests with a empty browser cache, which is the case when totally new visitors are hitting your website.
Definitely useful, if you are planning to expand your website and want to see if your current web server can handle additional traffic, or you need to start searching for a new one.