Load average is an easy number to monitor, so lots of people focus on it. However, it doesn't provide you with much information. When your load is high, you have to examine other values (e.g. CPU time spent in user mode, system mode, and iowait) to determine why the load is high before you can start to resolve the problem. If you monitor and alert directly on those other values, you'll save time.
Exactly, looking at the load curves over time is useful to gauging how well you are doing overall and for spotting potential trouble issues but when it comes to actually dealing with these issues or predicting an eminent collapse i tend to look at mysql threads and performance, the slow query log, concurrent users, etc. for determining what needs to be dealt with and what will hit us on the head in the near future.
