Maybe it's just me but I found this "Security Feature" of Office 2010 a bit annyoing out of the box.  Outlook does not download any pictures by default for HTML emails.  Now this is nothing new, but what is different is that Outlook 2010 has added another layer of security around the pictures.  You now have the option to finely tune when things are downloaded.  The side affect is that nothing is downloaded at all.  And when I would click on "Download Images" on an email, it still would not show the images. 

I found that I had to explicitly tell Outlook to download HTML images and then restart Windows.  It did not work if I simply restarted Office.  Again, maybe this was just me.  Here's what you need to do in Outlook 2010 to enable images for HTML:

1. Click on the new "File" tab
2. Click on "Options"
3. Click on "Trust Center"
4. Clicn on "Trust Center Settings"
5. Uncheck the "Don't download pictures automatically in HTML e-mail messages or RSS items" check box
6. Click the "Okay" button
7. Exit Outlook 2010

Again, for me I had to restart Windows (Windows 7 64bit, Office 2010 64bit) to get this to "take affect".