Before you buy from a web host, check their SLA and ask how they cover SLA breaches. Don't do business with a company that won't put their money where their claims are.
My host has:
If Liquid Web is or is not directly responsible for
causing the downtime, the customer will receive a
credit for 10 times ( 1,000% ) the actual amount of
downtime. This means that if your server is unreachable
for 1 hour (beyond the 0.0% allowed), you will receive
10 hours of credit.
Rackspace Guaranty: We will credit your account 5% of
the monthly fee for each 30 minutes of network
downtime, up to 100% of your monthly fee for the
affected server.