The only benefit of a floating menu would be a less intimidating interface. I used FastStone Capture and only recently replaced it with ScreenshotCaptor. The reason i replaced FSCapture is that this software is no longer freeware. What I liked most about FSCapture was the ability to add objects (arrows, notes) to the captured image. I must admit that when I first opened ScreenshotCaptor I was intimidated by it's interface. It took me some time until I discovered all the features I was looking for.
I only suggest a sys-tray context-menu redesign with icons for "Grab ..." items, advanced preferences in a sub-menu named "Options". Also "Help", "Check for updates", "Visit forum..." and "About..." could be in a "Help" sub-menu, as I rarely use them from the context menu and they take too much space.