I am not sure if tags based navigation would be easier for users. In our web we categorize software (like download.com) and categories maybe are hard to understand.
I personally prefer tagging to using categories.
The advantages of categories:
The advantages of using tags:
The advantages of using tagging is that the amount of tags something can have is unlimited, and ultimately users can tag items themselves. This is allows for a nice level of user-interaction, and your data will improve by each user adding a tag.
Navigation based on tags is then actually searching on any combination of tags, and will allow to get a very precise wanted collection of results. E.g. very good examples of succesfull tagging are (imo):
I think it depends on your audience, if they are young and tech-savvie then tags could work well, but less experienced users can find them difficult and much less browseable. There was a similar question on stack oferflow and one of the answers from a google interaction designer was useful to me.
The relationship between items and categories typically is one-to-many (in a typical taxonomy items cannot belong to more than one category), while tags are many-to-many (multiple tags for each item). Categories are most often predefined, tags can more easily be user-defined. You can even use both at the same time, although that implies added complexity.
Which is better for your application depends on the domain, characteristics of your users, and the terms they are familiar with.
Some questions I'd ask:
A pragmatic approach would be to test both. Take a subset of items, define both categories and tags, present these to some real people (in the hallway?) and watch how they react.