Well, I agree with almost everything SmokeAndMirrors says. I'm certainly not going to defend the Kindle in the field of the format wars. Locking the Kindle out of reading .epubs is just plain rotten.
However, druggist61 already has a Kindle, and now s/he knows how to get around the restriction.
Keeping customers blind to what they're buying, a la B&N, stinks too.
My only departure from SmokeAndMirrors is on how important the formats are when choosing an e-reader.
You spend untold hours holding and staring at your e-reader, giving no thought to file formats as you're lost in your books. For this reason, I believe the actual feel, look, and performace of the e-reader is of greater importance than the formats it reads, or the restrictions of its native online store. For example, I tried a relative's Kobo reader, and it felt heavier, with squared edges, compared to the Kindle. I preferred the Kindle.
By contrast to your actual reading, the time you'll spend on administrative tasks is minimal. Formats are a consideration here, and the Kobo's openess is a strong selling point. I just don't think it's as important as SmokeAndMirrors does.
In the original Beta v. VHS question, the OP wondered if he might be stuck with an obsolete device or formats. My answer is no. The interoperability here makes the analogy break down. It will take you a few extra clicks of the mouse (for conversion), but you can make your VHS ePub files play on your Betamax Kindle, and your Beta .mobi files play on, well, anything.
So anyway, try a Kobo, a Nook, a Sony, any kind you can get your hands on. It's only then that you'll see and feel the differences.