IE9's new tab page (or about:Tabs) is a handy way to access most frequently accessed sites. But if you'd like to display more than 10 sites -- there's no way to change the numbers in the options screen! Fortunately, a quick registry edit is all that's required. Microsoft's Eric Law, posted four .REG files which allow you to display 15 (3 rows), 20 (4 rows), or 25 (5 rows) of sites. The default IE9 default setting is also there should you decide 10 sites was enough after all.
If you're the DIY type and registry editing is right up your alley, pick your select from under:
Windows Registry Editor Version 5.00
Note: If you don't see NumRows listed, just add a new DWORD value and enter between 2-5 (Replace dword:xxxxxxxx): dword:00000005.
Or download the .REG files here.