Whatever the solution, you have to get staff to declare what it is on the front end. It's not all about the technology. I see some of the benefits of Sharepoint, but depending on your audience (tech-savvy or not) it may become a training issue. Prepare for change management.

What I like about Sharepoint is the Office integration, the improvements over the last few years, document history (versions), and mostly, the ability to require metadata. If you have a taxonomy of topics, it will make it much easier to create a search appliance that can find what people are looking for. You may be forced to look at auto-classification if you can't get staff to do it, or hire knowledge managers (librarians) to properly catalogue. Trouble for us is getting to agreed-upon taxonomies and hierarchies across divisions (I'm in the knowledge management trenches here).

A good way to start might be Sharepoint repositories, require a topic field, seed it with however many topics you can come up with, and leave an OTHER field so you can collect what you have not organized. If you analyze what comes into the OTHER topic, you may keep adding new topics.

Find the logical buckets to start search before they think about searching too. Does your staff only care about 1 project at a time, break it up into project searches. Basically offer them one level of selection before they get to search - it may make things easier (if you are structured that way). They may look for something from a particular function - Marketing search vs. Operations search.

Also, sharepoint can leverage active directory info, so you may be able to get some metadata automation (Docs from sales staff vs. R&D, etc.)

Hope these points help. Contact me if you need more.