Hey Tom, glad you found it. I haven't had any feedback from anyone using the CSV tab as yet so I'll be interested to hear how you get on and find it all. Please post back any thoughts.
It is a 50/50 call whether in this case you might be better off doing the upload of excel to Goodreads (presuming you can get your spreadsheets in a format they will accept). The biggest challenge time-wise you are going to have is finding a goodreads id for all those books.
Fundamentally you have two choices. If you upload to Goodreads from Excel, then of course you will be using the goodreads web pages to find matches for those books. I haven't used the functionality so I don't know how well or easy that is. You might want to try it on a small sample just to test it. Once you have those books on a shelf in goodreads, then you would fire up the Goodreads Sync plugin and setup a sync from your shelf. When you do the sync, it will then give you a plugin screen showing you all those books and any matching books in calibre - if there is no match in calibre automatically made (either by goodreads id or isbn) then you have the option of creating an empty book for it. This is all the most time consuming part of the process - "linking" a book in calibre with a book in goodreads. You do it once and then never worry about it again. Once you have created those empty books, you will probably do metadata downloads for them to populate all the extra stuff you are missing like descriptions etc.
The alternative approach which is what you have cottoned onto here is to use Import List to import your books from a CSV file (exported from Excel of course). Then you will have this plugin wizard screen to match against any existing books in calibre and the option to create empty books for the rest. You might then do a metadata download to fill in all the rest of the data for them. Your next step would be to then use the Goodreads Sync plugin to add those books to shelve(s) in Goodreads. When you add to a shelf, it is going to check whether each book has a Goodreads id linked to it - if you have used the Goodreads metadata download plugin you will already have one, otherwise it will try to match by ISBN and worst case you will have to interactively use the plugins ability to search goodreads for a matching book.
Either way, for 2000 books there will be a little time involved, and it comes down to how fussy you are about which edition you want to link to on Goodreads (something you can always change later using the Goodreads Sync plugin), which matching algorithm is better based on the quality of the data in your spreadsheet, how many books you have in calibre already and whether you have been using the Goodreads metadata plugin already on them etc etc.
As I said do let me know how you get on with this plugin if you give it a whirl.
Edit: I just read the fine print on the Goodreads website. Uploading to them is only an option if you already have an ISBN for each book in your spreadsheet. Guess that answers the question as to how their matching logic works
