The major push in today's world is towards cloud or SaaS computing.
With that in mind a lot of major applications including SalesForce (CRM), Google, Parature (helpdesk), etc expose their applications via web services.
It isn't just a good idea, it's the only way to have your application taken seriously by companies looking to integrate it into their environment.
That said, the only example I can think of when utilizing web services to wrap your DAL is bad idea is when only one application will call the DAL and it is under your direct development control. This is due to the performance penalty paid for serializing/deserializing the data across a web service boundary.