Does autosave do a full save to dwg format?
I was always under the impression that autosave was an emergency only option, and should only be re-named and used in the direst of circumstances.
Yes it does. The only difference between a dwg and an sv$ is the extension. There is nothing unsafe or scary about using an autosave.
Indeed. The way I understand it, ISAVEPERCENT dates back to a day when disk drives were considerably slower than they are now. Basically, when you would open a file that you had previously saved, Autocad would only write your new modifications to the end of the file. So when you ERASE an entity, Autocad would not actually remove the reference to the entity from the DWG file, it would just append a note to the end of the file saying that you had erased the entity. Then, the next time you open the drawing, it would parse the file consecutively, creating a reference to the entity, and then erasing it.
Obviously, this creates "wasted space" in the DWG file. Autocad can estimate the amount of "wasted space". When this value gets above ISAVEPERCENT, Autocad will save a completely new version of the DWG file, which completely omits references to the erased entities. This completely cuts deleted objects out of the DWG file, but takes longer than a "quick-save", which can simply append some data to the end of an existing file.
These days, computers tend to be fast enough that there's usually little reason to keep ISAVEPERCENT at anything other than 0, unless you work with very large files.
But the part about not trusting Autocad's default Autosave files is right on the money. Autocad tries to "clean up" Autosave files, and it may delete the Autosave before you get a chance to use it. Similarly, something about saving a RECOVER file seems to delete the Autosave files, so if you attempt to do a RECOVER, you will likely lose your Autosave file unless you grab it BEFORE you tell Autocad to try saving a RECOVER file.
With Civil-3D, at least as of the 2007 edition, Autosave is basically useless, because attempting to save a drawing while parcels are being edited causes problems. Unfortunately, Jeff's routine (and the others like it) also suffer the problem. Turning Autosave completely off is the only way to avoid the issue, at least without getting into more-complicated code that checks the integrity of parcels before doing the save. Hopefully Autodesk fixes this problem soon (hopefully it's already fixed in 2008...?). Even though the Autosaves are very untrustworthy, they are sometimes helpful.