An accident near Rackspace's Dallas datacenter sparked a late-night Web crisis, downing Internet service providers from Texas to California and bringing down 37signals' Web-based software suite, on which many startups depend for coordinating their work. But Rackspace worked fast to fix the cause of the outage — balky chillers which failed to start when switched to backup power, causing the datacenter to overheat — and by midnight, most of Rackspace's hosted websites were back online. Here's the apology note from Rackspace CEO Lanham Napier, forwarded to us by a customer.