My host allows unlimited subdomains. Also "forum.xxxxx.com" or "xxxxx.com/forum"? What are the pros/cons of each? Does it even matter?
blog.xxxxx.com is a completely different domain, so I think it's better to go with the xxxxx.com/blog/ route so there is a better consistency with the pagerank and links. I've never done a blog.xxxx.com type setup, I always use xxxx.com or xxxx.com/blog/
having it on a subdomain will allow you to host it on another server if needed also. I like the idea of having a subdomain, but dont really think it is worth it.
I agree with the idea. Also the second level is not too deep from the route directory as far as crawling by search engine spiders is concerned