Where can I get the IE8 Beta?

Here's a nice short link: www.GetIE.org

Known issues

IE7 "Strict" pages fail to render correctly? 
Windows Update blocks IE8?

Click the "Emulate IE7" button in the toolbar.  Restart all instances of IE.

IE8 user-agent is blocked?

Check out the UAPick addon.

Right-to-Left HTML is not yet implemented

Right to left support is not yet implemented. 

Closing IE via CTRL+W or File > Close leaves zombie iexplore.exe processes around

Solution: Close IExplore via the "x" or Alt+F4.

Use taskkill /f /im iexplore.exe to kill all IE instances, including the zombies.

Tips and tricks

How can I tell what rendering mode a page is in?

Right-click this link: ShowDocMode and choose to add it to your Favorites, inside the "Favorites Bar" folder.  

When clicked, it pops a message box showing the current documentMode for the document currently displayed.

                If it shows 5, the document is in IE5 / Quirks mode.
                If it shows 7, the document is in IE7 Strict mode.
                If it shows 8, the document is in IE8 Standards mode.