I doubt this would be a problem for most customers. Even the Level 1 plan provides 20GB of storage and 1000GB of traffic, enough for quite a few 'normal' sites.
One other thing worth mentioning is the CPU resource limit. There is a limit of 60 CPU minutes per plan. This is, as far as I know, shared among all the sites hosted under that plan. This is to prevent an extremely popular site (or an extremely inefficient site) from slowing the server for other customers.
In reality this is unlikely to be a problem for those with only a small or medium number of sites hosted, but it could be a problem if you take the 'unlimited domains' literally and host a great many sites.
Pay just [color=#CC0000]$22.40[/color] for 1 year Dreamhost hosting, use promo-code [color=#CC0000]MOJO97[/color]
Save [color=#CC0000]$97[/color] on all 1 and 2 year plans!! (Max saving on monthly plans too!!)