Sunbrella just introduced a new 10 yr limited warranty (previously 5 years)
With proper care and maintenance you should expect a minimum of 10 years use.
Furthermore the less the fabric is exposed to the elements (mostly the UV) the longer it is going to last.
Check out
http://www.youtube.com/watch?v=XVXV2qc0CRM for cleaning instructions
As for thread you should use a PTFE (Generic term) or Tenara by Gore (Brand Name) this type of thread is guaranteed to outlast the fabric.