I recently signed up for Trello (excellent on-line collaborative to-do lists) and added trello.com to my speed dial in Chrome (I'm on the latest version).
Even though I've visited the site several times using the speed dial ("Preview is not ready, click to create preview"), it hasn't created a preview yet, any ideas?
Since there's a conflict between the latest Chrome and Speed Dial (I've logged the issue with the entension author via the Chrome web store), only on https pages, I've found this work-around.
I located the directory where Speed Dial installs to (thanks @Synetech). On Windows XP should be something like:
C:\Documents and Settings\[My username]\Local Settings\Application Data\Google\Chrome\User Data\Default\Extensions\dgpdioedihjhncjafcpgbbjdpbbkikmi\2.5.1_0\images
Although there were no thumbnail images in this folder, I created my own folder under images entitled "mine": ..\2.5.1_0\images\mine
I then copied a screenshot I'd taken using Google Screen Capture into this directory as "trello.png".
The last step was to go to "Edit Dial" and type "images/mine/trello.png" into the "Dial Image URL" box (you can also load images from any url such as photobucket).
Clicking save then immediately displayed my screenshot as the thumbnail.
You have to be patient; it will eventually update it. Several of the sites in my most-visited list got broken-site thumbnails because I tried to visit them while disconnected. It has been a few days since then and a couple of them are still showing the broken page preview while a few others have updated.
(If you really want to know what triggers and times Chrome uses to update the thumbnails, you can peruse the source code.)
If you are impatient, you can try to force it by deleting the file Thumbnails in your user-data folder, but it may still take a few visits before it updates them.
