You can download and install the Barnes & Noble eReader on your computer, iPhone/iPod Touch, or BlackBerry. I used it before on my laptop and BlackBerry. (No need to lend it to yourself...just use your B&N login when you set up the eReader on the other devices.) You have access to the eBooks you purchase from B&N but, of course, not the ones you sideload onto your nook (e.g., purchased from sites other than B&N, borrowed from online library, etc.).
It does what it needs to do with the exception of a couple of things that I didn't like which may have been fixed/updated by now. When I resized the font on my laptop to the larger sizes, I would lose several lines from the bottom of each page. (It's like the eReader program made the text larger but didn't adjust for the additional lines it would take to display it on a page.) The other one was that there was no syncing that I could find, so that when I read ## pages on my laptop or BlackBerry, when I went back to the nook, I was back to the last page I read on the nook...and vice versa.
All in all, it just didn't work well enough for me to stick with it. (Of course, that's just my opinion.) I just preferred reading on the nook a lot more than I did on the laptop or BlackBerry. And there weren't enough occasions where I could use an alternate device to read my eBooks as opposed to just taking my nook with me.
I'll have to tell a friend of mine in the office that he can download the Barnes and Noble eReader to his Blackberry.