If the hosting provider has a reasonable offer for registering the domain and hosting combined, I don't really see a problem with doing that. I would just make sure that if the hosting wasn't what you expected, that you are able to transfer your domain out without fees, etc.
The reason I register my domains separately, is because I have a lot of them and I like to have one account to just overview them all where I can flip back and forth between different hosting providers without having to go through the hassle of transferring domains.
I have seen several threads that it is better to avoid registering the domain and hosting the web site at the same place, but I do not really understand how critical it is. I am about to choose HostMonster as my hosting provider, and they offer free domain registration. Is it OK also to register domain with them, or it is better to register separately with someone like GoDaddy and then park the domain at HostMonster?
Thanks for replying!