Shelfari user. Although I don't utilize all the features (I don't keep my wish list on there, and I don't have my entire book collection on there yet), I do try to keep it up-to-date with the current books I've read and added to my library at home.
However, I have found a site to play on!!! I belong to the Harlequin/Silhouette message board, and a poster on that board, Gail, mentioned this new site where you can keep track of your series. With Shelfari, you add your books in the series and then have to create a tag to keep the series together. Then you still don't know which book comes next...you have to investigate that either on the authors' websites or other sites that track series. BUT...there is a new site out there where you can track your series...the books you've read and which book comes next!!! It even lets you know what is Coming Soon.
FictFact is my new playground. Another great feature is you can follow other people and see what series they are reading. If you can't find your series on the site...just email them and they will add it. Gail tried that out, and her request was added the next day. So far I have added 26 series, and it has calculated that I have read 45 books out of those series. I know what book I need to read next and that is a big plus for me!! You can search by author, series, book name, and most popular series. You can recommend books, search their book calendar for new releases, and set up your own profile. I could go on and on about the features of this site...but I won't...you have to see it for yourself.
So, head on over to FictFact and try it out...you won't be disappointed.