See, this is something I have thought a lot about. I can understand the value of the 'enterprise' pricing tiers (and yeah, if I have to do a bunch of paperwork, it's totally fair for me to charge you more.) So I can see where pricing tiers could be a good thing.
However... the bit I'm questioning here is how far you distance your 'enterprise' product from your 'geek' product- Especially if you have a strong 'geek' following already, I would argue that you don't want to start over in the 'enterprise' space. You want to carry over the name. Either, as Patrick suggested, move the 'geek' product to a less-accessible URL and professionalize your primary brand, or build a "tarsnap enterprise business edition" url.
Either way, there is a whole lot of value in a brand valued by nerds. I agree that brand needs to change some (and the product needs to change more) to be marketable to the enterprise, but... the boss basically respects his or her geeks... enough to pay them a lot of money. Sometimes I even find the business folks emulating the geeks when dealing with computers. A MBA where I worked saw how paranoid I was about ESD and asked for one of my wrist straps. He used it while he was typing emails on his mac. The "business edition" of the thing his geeks say is awesome is going to have a lot more pull than just some random new brand.