I was lucky enough to get the keyboard edition without 3G before they stopped the sale of them (now its keyboard and 3G or the nokeyboard and no 3G only - though second hand you can still pick up keyboard and no 3G if you want).
Personally the Kindle, in my view, is aimed at doing one thing, letting you read books start to finish. And for this its fantastic, e-ink is seriously good and lacks any of that harsh glare that LCD screens have (heck I spent 10 mins trying to peel off the seethrough text sticky label on the screen front before I worked out that it wasn't a stickon but was the screen!) Personally I think the 3G feature on its own isn't worth the cost since most of us are going to be in countries where you can easily get access to your home computer or to a cafe or even free wifi hotspots - so its a neat feature but not essential (esp in what is essentially a book).
The keyboard though does make a lot of difference for making notes or adding sections or any form of typing required, not sure if its a deal breaker or not. Also note that the no-keyboard edition has half the memory capacity of the other, so reduced storage is another consideration (though even at half you'll still get a heckload of books on there).
The other great thing is getting to access books from the free (legal) websites - there are loads of copyright free publications worth reading that you can get for 0 costs (eg all the works of HP Lovecraft as one example). Just load up the texts into the unit and read away. Personally I use Calibre which is a free ebook software manager on the computer - small to install and lets you manage ebooks and text documents on the computer and on your unit (it even detects and integrates with it when the kindle is cable connected to the PC to let you transfer). You can also use Calibre to convert text documents to the mobi format for the kindle as well as alter book meta data (note this is for copyright free works - books bought through Amazon are managed at the Amazon end and come with suitable copy protections and the like).
On the subject of Amazon remember all books bought there are tied to your account, not the unit - so you can remove and add them as you choose (should you find you need to free up storage). Further, barring exceptional situations, books bought remain active even if they are later withdrawn from sale on Amazon.
Downsides:
1) Its not that good with pictures - though part of this is that many books are shipped with no or pretty poor scans of pictures/cover art at present (which is somewhat dissapointing). However in general it can be a bit of a pain when viewing maps (fantasy books) and for trying to read regular maps I'd far far prefer paper or at least a larger display (works in a pinch but not ideal in my view).
2) It's not that good with PDFs - which it treats like a picture and is a nightmare since unless you have the size set very small you'll have to scroll left to right to read each line. Personally I convert PDFs into text format so that I can read them (it then only gets a little confused with charts/diagrams present). The USA has an overside kindle that is better for PDF reading (Because of the larger screen).
3) You can't custom set your own backgrounds when in idle mode - this is a darned annoyance as the regular ones are dead boring and all have the "slide to turn on" notification on them - one is even an old printer with "please email us your thoughts" on it! You can hack the kindle unit open to change these custom settings if you so choose - though of course this voids warranties on the unit.
4) Amazon is bound and limited regionally and as such some books might not be available in your country even if they are sold by Amazon in others. Far as I'm aware this is a publisher more than Amazon alone.
Links:
Calibre
http://calibre-ebook.com/
Amazon classics free ebooks: [url]
http://www.amazon.co.uk/s/ref=amb_link_157483207_1?ie=UTF8&node=434020031&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_s=center-5&pf_rd_r=09PHN2ANE31NMK4PR6B9&pf_rd_t=101&pf_rd_p=220353107&pf_rd_i=434020031[/url]
Internet Archive: [url]
http://www.archive.org/details/texts[/url]
Open Library [url]
http://openlibrary.org/[/url]
Project Gutenberg [url]
http://www.gutenberg.org/wiki/Main_Page[/url]
ManyBooks.net [url]
http://manybooks.net/[/url]
arthursbookshelf [url]
http://arthursbookshelf.com/[/url]
contains a range of books in various formats (ePUB, PDF and mobi) these also often contain plates and cover art!