Just as every hosting provider it has of course downtime. I get maybe an average 1-2 days in total per year (a few hours here and there). I do know some others sometimes have more when their servers realy breaks down.
Dreamhost has many very big advantages over all others. Great support, very open policy regarding server/downtime at dreamhoststatus.com and many, many more things. I have had overtime about 10 providers, but now I have been with DH for over 5 years. The best one ever for a very low price.
You will have a 97 day money back garantee, so what do you have to loose. Give them a shot.