Bookworm is a nice open source reader, but the question remains how big is its book library, and what are the terms under which you access the material?
The Amazon Kindle has found a niche because Amazon makes certain that channel is filled, with the books people want to read. Despite this success only 500,000 of the original Kindles were sold.
Compare that to the number of human readers and it's clear that eBooks remain at the very front of the demand curve. We're still with the gadget freaks and the hobbyists, not the mass market.
Before the mass market grabs any eBook reader, whether open source or not, the business model has to become acceptable to book readers, and comparable in value to real books. These eBooks must also become ubiquitous, as real books are.
The short version is we're still focused on the razors, when we need to look at the blades.