I'm a Kindle nerd and love it. I think it's flat out amazing. And I'm a fan of Lonely Planet. After some rough points in the last few years, they're back near the top of the pack. I also fly over 100,000 miles a year for fun, so I'd like to think of myself as a slightly experienced traveler. Having said that, I'm not sure I'm sold on the concept of eBooks for travel.
The eBook itself is a lot better laid out than slightly older "... On a Shoestring" eBooks by LP. It has color photos, lots of hyperlinks so I'm able to click around rapidly (from Index to Venice to various things in Venice) - makes it great for armchair exploration. The color photos look awesome on the Kindle Fire. The book also includes Morocco, which may or may not be in Europe.
The content itself is fairly consistent with LP's standards, Thomas Kohnstamm not withstanding. If I were planning a long European adventure, this book would be definitely part of my arsenal of books, along with others and information from online sources (Wikitravel, for instance.)
Lonely Planet also offers PDF maps on their website for other eBooks, but not as of yet for the Europe on a Shoestring eBook. I'm assuming that this is forthcoming, but I'd find myself either printing out lots of copies of maps or relying on the Kindle Fire to view them. If you don't have a Kindle Fire, I'd suggest getting the paperback copy of Lonely Planet Europe (Shoestring Travel Guide) - I quickly deleted off my Kindle Keyboard because it was slow and navigating around was a pain.
I'm of the camp that believes that a paperless travel guide is like a paperless toilet - not something I want to really do. Maybe it's just that I've spent a fair number of years with paper guidebooks that I can jot notes in, carry with me independent of worrying about power and share with a fellow traveler after I'm done. That's not to say that this book is worthless - quite the contrary - it's great to have it all in a digital format that won't weigh you down if you need multiple books. It's all going to boil down to personal preference. Either way, you'll have a vast majority of the information you'll need to navigate around Europe on the cheap.