Server Error in '/' Application, sharepoint timing out or very slow, usual suspects?

This morning I arrived to find out that our intranet had been unavailable for an hour and a half. It would take several minutes for the homepages to load, or they would time out:

We rebooted the WFE and SQL servers, and everything seems to be back up.

Please note that I don't want to extend the httpruntime executiontimeout in the web.config.

I'm trying to identify the cause. Any recommendations on what to look at in WFE, 14, and SQL logs?

Thanks