I got the Kindle in September 2010. The timing was based on the fact that I had a baby on the way (more on that later). Because one of my hobbies is reading, and I realized that I was going to soon have considerable amount of time that I would be stationary, with only one hand available.
I already had a fairly large collection of e-books, mostly Adobe Acrobat files that are the daily nourishment of an academic. But I was also exposed to ebooks on my mobile phone and my long dead Palm Pilot. So I was used to the concept.
So what have I found? Like other data devices, the Kindle is an adjunct to my computer, not a replacement. Where it shines is in it's ability to sync with my computer, in particular I probably use the Kindle to read news as much as to read books (through pulling in news feeds in Calibre).
For books, I like the fact that there are lots of inexpensive books. One of the first books I bought for the Kindle was Sears' The Baby Book, which was a $5 special right around the time my son was born. I regularly check Amazon's discount section for similar gems. But the shining jewels are the free book depositories. Project Gutenberg with it's vast collection of older works, with the better offering conveniently arranged into topical bookshelves and the Baen Books Free Library and their many CDs of books available.
I am a particular fan of Project Gutenberg Children's Picture Books which have provided a fine introduction to the tales of Peter Rabbit and many friends.
The place I really appreciate the Kindle is when I'm holding my son, when he is sleeping Because my son likes to be held when sleeping. And reading is a good way to use the time. The Kindle is light enough and small enough to hold in one hand, or prop it up on my son without waking him up. And I can work its controls while doing so.
The other way to get something on the Kindle is email. Every Kindle has a firstname.lastname@example.org email address and you can send a file to yourself (after setting up your account so that it will accept the email). I do this to send notes (e.g. shopping lists) or documents to myself so I can look at them online.
PDF is awful. Because PDF is a fixed size, and the Kindle has no easy way of moving around the page or zooming arbitrarily.
Wifi works, but it is slow. Use sites that are optimized for mobile use is available. When the page is loaded, use the Kindle menu to switch to 'Article mode', which strips it down to the article itself (i.e. takes out all the navigation and advertising columns)
Final verdict: Very handy. I would recommend it to any parent who reads, because this will help keep you sane when you are trying to do anything else when with a baby. Also very handy for carrying around documents without carrying lots of paper.
Resources for Kindle
Calibre - Library manager for your ebooks. Manage all your ebooks that you do not buy from Amazon here , it has a RSS feeds and it will automatically load to the Kindle when you sync. That means you can automatically download stories from news sites, blogs about any topic of interest.
Send to Kindle - Chrome plugin that automatically takes any web page and emails it to your Kindle (assuming you have set it up with your email address)
ReKindleit - Plugin for Firefox. Same idea, when you are looking at a web page, email it directly to the Kindle.