I am adding a blog to my main website, and I've been debating whether to add it to the same URL or if I should create an entirely new one. It should get a lot of traffic fed in from my main site, and I expect the links to come, so I was wondering if it would be better as a separate site. Thanks.
Same subject? I'd say either do a directory on your site: www.foo.com/blog, or as a subdomain: blog.foo.com. I don't know that you lose anything by having it on same site, or gain by having it offsite. I'm sure someone else may provide counterexamples, but I've mostly seen same site blogs unless the subject was going to diverge from the site subject.
I think it may be better to keep it on the same domain mostly for convenience for you as you don't have multiple accounts to manage. Not only that I think that subdomains benefit from the pagerank of the same domain and you avoid being put in Google's sandbox as you would with a new domain.
You know, I'd have never thought of the issue with the GoogleBox. I'm currently waiting for google to reindex my blog, since when it last looked at my site, the blog was in a subdirectory, and the main directory didn't have an index.html. I do a search for my site and I see it has included my public_html directory. I'm now waiting for it to rescan my site, so things will actually be up to date.
This decision depends only on why you are creating the blog. Is it to augment the website topic or start a new one? Once you answer that question you should have the answer to your other question. Of course bear in mind that a new domain will need to go through sandbox issues, but if you stick to it you do have two sites in the long run, which you can drive traffic back and forth between them.
If you can afford to wait to get indexed, then a seperate (but related) site could be better in the long run (especially if hosted on different servers). If this is something that you might ever spin off in a different direction and/or sell one but not the other, definately put it on a different domain.