Thanks for the great work you've done on the iPad import features. The plugin works pretty well. However, I do have a suggestion - I don't know how challenging this might be, or how useful to anyone other than me, so I'm raising it as a discussion point.
Currently, the first tag in the book's list of tags is converted into an iBooks category. This seems like a sensible choice in many cases. However, since iBooks has no reliable way of interpreting series, might it be more useful in some cases to convert the series name into the category? Or perhaps to fall back to the series if there are no other tags to convert into a category?
On the upside, it'll make the task of locating a series of books easier - currently if they have differing authors, it's virtually impossible.
On the downside, it doesn't solve the problem of ordering within a series.
This might provide a partial workaround until some form of title renaming becomes available within Calibre, which looks like the only method that will really work until iBooks is one day updated to recognise series (I live in hope!).
Just a thought... feel free to criticise.