I have one of the older versions and really like it. I have a whole bunch of books on it and also get the NYT every morning. Since I can't get the print addition delivered in a timely manner, this is great.
My Kindle is the version that allows a memory card. My understanding of the newer one is that it does not.
I have not tried uploading any documents (in .pdf format) via the email process, so I can't tell you how that works.
I have not had any major issues with it. Most of the books I want have been available. It is great for travel and sure beats the heck out of hauling a bunch of them around. I am a voracious reader normally and this has been a wonderful treat.
Drawbacks include the page turning buttons being to easy to hit accidentally requiring me to go back. The scroll wheel/select button is a bit clumsy. It also does not have a backlight, so you have to provide a light source just like with a regular book.
But, it is easy to read and a pretty cool device. It doesn't take much time for a book to be delivered once ordered and the new version is supposed to be faster.
So, it does have some drawbacks, but the benefits outweigh the shortcomings.
I don't want to upgrade yet, but if I do, I will let ya know, Andy.