Isn't Mercurial Suitable for a Large Project?

Today I tried Mercurial-1.1 and Mercurial-1.1.1. This was the first time for me.
I have known Mercurial since 1 year ago. In these days, I will have to write some codes and manage documents about my research. For the sake of that, I would like to use Mercurial.

Mercurial is a distributed revision control tool allowing distributed parallel development. The idea is useful because I can commit any changes into local computers and merge them at anytime on-line after that. It's not possible by using traditional SCMs like Subversion.

However Mercurial seems not to be mature yet because when I merged and resolved differences following the tutorial and guessing what the tutorial didn't describe, a resolved flag for a merged file wasn't turned off after commit command. And the behavior of conflicting merge was different between 1.1 and 1.1.1 even though the release note of version 1.1.1 didn't mention the fix.

The most important question is about that "What Mercurial can't do" says "you cannot check out only one directory of a repository." Although Mercurial is for distributed development, does this description mean that Mercurial is not suited for a large repository which causes huge amount of file copies to create new clones over Internet?

Anyway, I will continue to try Mercurial because I think that it is an excellent tool which enables to work anywhere even though I am offline...