All virtual servers are running in a datacenter.  You should inquire about the datacenter sinces its location and infrastructure can impact uptime and performance of your virtual server.

Datacenter Uptime  –  Depends on:

• Internet/Bandwidth Providers  –  The best centers have multiple providers blended together to guarantee uptime for your virtual server hosting.
• Power Redundancy
  • Multiple Power Feeds to the center
  • UPS (Uninterruptible Power Supply Units)
  • Generator Backup Power  –  with fuel contracts
• Location  –  Is the datacenter located in an area with little or no weather threats (hurricanes, earth quakes).
• Is the center staffed 24 hours a day 7 days a week for the few times a hardware issues arises?