DH has downtime - if this is very important go find something else, more expensive. You can get an idea of how often on http://dreamhoststatus.com/ - just remember they have quite a lot of servers. As you see they are quite open about it.
On DH, and anywhere else, do your own backups. DH has a monthly total backup you can ask for, but you will typically need to backup more often.
DH is cheap for the services offered, but generally worth the money. But you can definitely get better and more expensive webhosting elsewhere.