I think Gort has hit the nail on the head. I tried that link you provided to the mobile version of the gutenberg site, it loaded up no problems for me, and this time the book downloaded without any problem. It appears on the home page as the book title and not the generic .mobi filename.

I just checked, and www.gutenberg.com is also now working from the Kindle Keyboard with no computer required.

Of course it is easier to use http://m.gutenberg.org/.

When this thread first opened, neither site was working for Kindle Keyboard downloads. Somebody has to have fixed something.

To review what this means: If you have a Kindle Keyboard 3G, you can, almost anywhere in the world, regardless of WiFi availability, download for free, from gutenberg.com, most halfway popular books if they were published before 1923. And when in a life + 50 country like Canada, New Zealand, Korea, Japan, China, and dozens of others, you can legally download the best books by authors who died before 1963 via gutenberg.ca and mobileread.mobi. My non-lawyer understanding is that you can then, legally, take your eReader, complete with new downloads, to home countries with long copyright periods such as the US and UK. This is part of what makes me a great enthusiast for the Kindle Keyboard 3G. I wouldn't give that up for a better lit screen.

To summarise, there was a problem caused by PG server policy changes which has now been fixed.

See Amazon.co.uk Customer Discussions thread
Gutenberg to Kindle, has something changed?
http://www.amazon.co.uk/gp/cd/t/Fx3I...L6EW27HDIDKZ/2

I checked that it failed (and now works) using my Kindle Keyboard 3G and Kipling's Second Jungle Book (no images).

Yup, I banged my head against this for about two months for a friend of mine.

I can confirm that certain parts (.txt downloads IIRC) of Project Gutenberg downloads were indeed hidden when accessed for the kindle keyboard browser (this was about 3? months ago) tested it side-by-side, on the Kindle Keyboard, and a PC: it was clear to see that the page was rendered/served out differently by the server, rather than anything the device was doing.

Hopefully this is now fixed. I have had no issues since switching to the touch.

: )

If you happen to live in a country where the Kindle 3G has unrestricted web browsing enabled. In many countries, it's restricted to Amazon and Wiki (although most of the classics are of course also available for free download at Amazon).