First of all thanks for your comment :-)

Regarding your first question about the granularity threshold, I really don't have a golden rule, it's all about ~~feeling~~.\\ 
Mainly I tried to model the "Language" used when talking about blogs and wikis logic where things like "Post" and "Comment" exist, but things like "text" or "image" don't (those collapse in ~~information~~). But like I told you it was mostly about common sense. 

{quote:m4ktub}
About the domain models, why isn't post a wiki page? Are you already considering presentation issues here? 
{quote}

Well no, I'm not considering any presentation issues here, actually I haven't yet thought anything regarding presentation using this model.\\ 
The Post entity isn't a subclass of Wiki Page, because a Wiki Page may contain an hierarchy of other wiki pages, this means we can see a Wiki Page as a container. On the other hand, and in my opinion, the entity Post is an element. That means that I don't want to have an hierarchy of Posts inside other Posts, or Posts with other type of wiki pages. That's the reason why I didn't model Post as a Wiki Page.

{quote:m4ktub}
"Converting" the concepts of the entry/meta data model into web pages requires a whole sub model do be described.
{quote}

Couldn't agree more! That's something I still have to think about though.

Strangely your epiphany sounded very similar in some parts :-) But regarding the Blog being or not an entry. \\
When I started sketching this model, actually, the Blog was a subclass of Entry. But then I realised that a blog doesn't have historic, access control or comments. Those properties are only in the posts that are contained by the blog.
That thought created a "driving force" to take the Blog out of the Entry class hierarchy and make him a ~~collection of posts~~.

But like I said on the post this isn't ~~The~~ but a model. Model that can be flawed. If you would put Blog in the Entry class hierarchy, how would you do it? 

PS: Regarding snipsnap'p wiki syntax you can always check, [snipsnap-help] ;-)