Just because you haven't found a use for Yojimbo doesn't make it a useless product. I use and like Yojimbo a lot and here's why.
First, with respect to Backpack et al, I simply don't trust those web based services with my private information like passwords and the like. Indeed, there are a ton of tools that do this. However, this is the first such tool from a company that I trust, BareBones.
Next, the private information is strongly encrypted before storage on the hard disk or through .mac. The information can be safely and securely stored on .mac. If my hard disk craps out, the info is safe.
Finally, I use a number of Macs and need to have some information synchronized between them - especially the net password info and the like. Yojimbo does that through .mac with absolutely no effort. Any changes I make from any machine are reflected effortlessly to the other machines.
Thus, I find Yojimbo an incredibly useful product. I'm sure that there are lots of people who won't need it. I, however, do.
Now, can it be more useful - surely. However, its a v1 product. Cut em some slack for gods sake.
Productivity Was Never This Unproductive: A Review of Yojimbo