I use Dropbox to get ebooks from my computer / calibre to my Nook Color and Android phone (thunderbolt). I use FBReader to read the books on both of my devices, and FBSync to keep them synced. The great thing about FBReader is I can set it to look for ebooks in my dropbox directory on the tablet/phone, and then I don't have to do anything else in FBReader to get the books to show up.
I have set my Calibre library folder to be inside of my PC's Dropbox folder. I have about 750mb of ebooks, and when I add a new ebook in calibre it automatically gets sent to the dropbox "cloud".
On my tablet, I download an ebook using the "dropbox" app. Then I open FBReader. The first time I ran FBReader, I went to "Menu/More/Settings/Directories" and change the books directory to "/mnt/sdcard/dropbox/Calibre Library". This sets FBReader to use its default library folder as the Calibre folder that is created by Dropbox.
Now whenever I use calibre - it puts the ebook into my Calibre Library folder. I then go to the phone/tablet and use the dropbox app to download the ebook (hold your finger down on the .epub file and select download). Then I run FBReader and my book is in the library. Note that FBReader by default opens the last book read, rather then the library view because 99% of the time you open the app, you want to just continue reading, rather than switching ebooks.
If you don't have a dropbox account, GET ONE! They are FREE!
you can even use this
http://db.tt/kWGQPtl to get one (and give me a few extra MB's of storage!)