a host will do maintenance daily but it should never affect clients...the only time clients should notice something is if there is third party maintenace that is not always easy to avoid but if your with a good datacentre and good bandwidth provider normally they setup things correctly the first time and things are fine from there
the perfect host will setup a client and the client should be able to go with out ever needing to contact support accept for when they need domains or emails added
thats what my host aims for anyway