Ok, so why I won't probably switch to your service? ;-)
Currently, I use two bookmarking sites:
- Instapaper - this is for the stuff I want to read later, but not necessarily "bookmark" it, and
- Google bookmarks - for the stuff I might want later, so I want to bookmark it
Now, as I see it, the only advantage of historius over Google bookmarks is, that I can historify by one click (like Instapaper). But, this is not that important to me, since when I want to store something, my current habit already is that I always want to add a tag anyway. Because, despite Google bookmarks also having a search (in bookmarked sites), I almost never use it - I can recall an old bookmark by the tag more easily. Moreover, another advantage is, that I do not need another account to create, since I am also an Gmail user.
The third thing is, that I probably would not pay for bookmarking service monthly/yearly, when there is so much free offerings. Maybe you could convince me to one-time fee (like pinboard.in does), but probably not regularly.
So, to sum it up, your product combines good things from various other bookmarking services, but that alone doesn't make it better than others. You just need to find people, who like the workflow you are offering them with your service.
So to sum it up, my only advice I can give is - try to make your service available without need to register, so more people will try it.
As for registration, don't you need to specify a username when you use instapaper? The problem with using historious without an account is that some features won't work, plus you won't be able to access your account from a different machine/browser. Many users have requested it, though, so I'll try and make it happen!