Vi/Vim is, of course, an extremely powerful text editor, which is infamously difficult to learn. In my experience, it is THE hardest text editor to learn, often requiring several months before the new user feels that they are starting to feel comfortable with the new tool.
Even as recently as a couple of years ago, this kind of time investment was worthwhile, if you were a programmer, who had to spend a lot of your day in front of the computer, juggling different graphical text editors who provide only half of the features set you need for any language. There was nothing this powerful available.
Unfortunately for vi/vim, now there certainly is. Editors like TextMate now have a much gentler learning curve, while still providing the user with a fantastically wide feature set, and an amazing level of customisation. Other editing environments, like Panic's CODA, have concentrated on a different approach, helping you save time not by filling up the editor with thousands of specific text-production features, but by combining the functionality of several pieces of software into one, which saves up even MORE juggling time.
This port of vim is certainly well done. It is stable, and more Mac-like than anything out there. It is still very powerful, but becoming less so, as other editors catch up, and start providing features which vim does not have. For instance: easy project management features (ie., having a folder view) would be a welcoming addition, which would not be too difficult to implement.
Vim does provide some wonderful text-production features, but that is ALL it provides. If these were coupled with some of the easy and time-saving workflow features now present in the majority of other text editors out there, then vim's steep learning curve would be more attractive. As it stands, the vast majority of users will prefer to use tools that are easier to grasp, and which - in the long run - will save them just as much time as vim would.