Well, I have crossed over the threshold. I have received the same question enough that I cannot avoid posting something on the subject. I have been trying to avoid this and skirt it for some time now. Like forever. Truth is that my scanned film does not reside in Aperture. Nope. I would like it to reside there, all neatly cataloged and categorized but alas it just don't cut it. Yet.
To be completely truthful - I have tried it. I really really have. I could even live with all my 35mm stuff in Aperture but since a giant portion of my scans are large format and medium format I don't bother doing anything different for my 35mm. The reason is simple - Aperture chokes on giant files. I am not going to name the exact size because there is no exact limit. Let it suffice to say that Aperture becomes extremely unstable trying to use it with a project consisting of a bunch of files in the several hundred megabyte range. Confused is a nice way of saying unstable. So I don't bother.
I do suspect that Aperture 3 or Aperture X or whatever it is called will be 64bit and probably fix this issue. It won't target film users/scanned files as the target market - it will do this because a lot of high end digital backs are approaching the size of my scanned negatives. That and if you chuck a couple of bitmapped layers into the mix in PS the size of even moderately giant MPIX cameras turns into really truely gargantuan. I also suspect the popularity of stitched files and HDR will drive this need as well. Hey maybe Aperture 3 will have that crap built in, who knows.
Now to the nitty gritty. I do use Aperture to catalog my film negatives - I do it with low res JPGs and lots of metadata but the big scans are not actually in the library and I do not use Aperture to tweak them. While we are on the subject, I do find it extremely useful to have a reasonable sample of my film library organized with appropriate metadata in Aperture but I do not have even close to all of my negatives scanned and indexed. I don't even have close to my favorites scanned.
I have not published my process for doing this mostly because it would seem completely convoluted to most people. And it is but I do find value there for the short time it takes me to put the JPGs in there. If anybody is interested at all I will post a short description of what I do and more importantly why I do it.