This is especialy useful for all iPad users.
I've been using Calibre for years and just stumbled on this last week.
Using my eReader I simply plug it into my PC and transfer books.
Not so simple with iPad etc.
With Calibre all you need to do is set up the "Content Server", easy peasy. When you first do this it will show 'Start Content Server'
Once you do this all you need is enter that IP number like this 192.168.0.16:8080 in Safary or any browser you use. This works with anything that has a browser, connected to your WiFi. Save it as a bookmark then everything is one click away.
You can set this permanently in Calibre Prefs.
Make sure Calibre is up and running.
Every bit of electronic literature I own is stored in Calibre. All formats epub, mobi, PDF etc.
All my manuals, cookbooks, magazines, notes.