– I did a fairly intensive scanning session and think (it was a few years ago now) it took a weekend – say 10 – 20 hrs roughly. A system like Readerware would be better than the Bookpedia software for a mass scan, because you can order a real barcode scanner (of course, you might have one you can bring home from the shop?) and that is quicker to scan with than lining up a webcam with the corner of each book. And, of course, Readerware is for Windows, whereas Bookpedia is for a Mac.
– One time factor is potentially bringing the books to the scanner – it was quicker to do 1100 books stored in the next room, than scanning the 500 or so CDs (at that time) which I had to bring up in batches from the ground floor to the office and then replace afterwards. The actual scanning of each barcode only takes a second or so, and you do it in batches of say 10-20 books which you then have to replace in your bookshelves in the right order! It can take Readerware 2-4 minutes to find the books and download the data for each batch of books – depending on the speed of your internet connection and how busy the databases are (and how many / which ones you select to be used).
– Old books don’t have barcodes (or ISBNs), and take more time to enter because you have to type the author and title yourself. The time I gave above included some manual data entry (maybe 100 books?); older books don’t tend to have their cover-pictures stored in amazon, which means your cover-collection will probably have gaps in it.
– Readerware is pretty good with German language books (it can read amazon.de’s database), Also the CD program is fine with German CDs. Other languages (Italian, French) are also supported, because Readerware can access databases in France, Italy , Sweden, etc. Character set support is sometimes a problem – Umlauts etc. sometimes get screwed up in the scanning/download process – it only happens sometimes and may even be a Mac problem, since Mac and Windows use different character sets. It is not a major problem, but you may need to check and correct the titles / authors after scanning.
– I think it is worth doing, especially if you can then transfer the data to a PDA or mobile phone to take with you when shopping – I seem to have more problems remembering which CDs I’ve bought than which books, but if you have several books in a series from one author, it sometimes helps to remember which ones I have already bought – especially if the publisher changed the cover, I sometimes ended up with 2 copies of the same book!

Let me know if you have any more questions – hope this helped!