Maybe it's worth mentioning why these would be meaningful improvements.
Mainly, I have a problem with calling it "seamless" mode when really all you're doing is dropping out the Desktop layer. If I have a few windows from my Guest OS running, and a few native ones from my Host OS running, "Seamless" should mean I can manage and switch between all these windows... well, seamlessly. But no. If I click on a single window from the Guest OS, all of the Guest OS windows and the guest's taskbar are brought to the front, because they are all actually still a single window, regardless of the trickery of dropping out the desktop background. This doesn't work right. I should be able to select just a single one. I should also have an individual representation of each Guest application sitting right where the rest of my programs are, because forcing me to use another taskbar defeats the purpose of "Seamless" integration. The Guest's taskbar is always being covered up by native windows, there's no way to reserve space on my Host's desktop for it, and it forces the user to be familiar with two separate desktop, window management, and menu systems that have no integration.
Really all you get by using Seamless Mode now is Full-Screen Mode where you can see through the desktop background. The way Microsoft is doing it with "Windows XP Mode" in Windows 7 using Windows Virtual PC is far superior to what VirtualBox is capable of right now. I just don't have that option because I hate using Windows.