Windows Vista did transparency right, in fact in my own opinion the theme is the most polished theme to ever ship with a version of Windows. However Windows 7 took a huge UGLY step backwards. The transparency in the start menu and title bars should only be transparent when the window is not Maximized. OS X made a similar mistake in their original release of leopard by having things transparent all the time. This creates a very ugly effect with certain wallpapers and sometimes readability issues with whatever is in the title bar. Please fix this before final release. Vista did it right when things are Maximized the dark colors with white text is very readable and the taskbar looks good in black to.
Fix the transparency issues. When items are maximized the taskbar and titlebar should NOT be transparent. This is an ugly effect and should be resolved by making a system similar to Vista's transparency, which as I mentioned near perfect in my opinion.
Perhaps the best solution is to provide an option to turn the transparency effects on Maximized windows on and off. Options options options.