Launching steam exe while steam running should...

[coladict]

At least a few times a week I have to terminate the steam process because from Task Manager, because it has no windows open, the icon is missing from the taskbar (yes, even in the extra icon list), but when I launch the exe it just tells me Steam is already running.

My suggestion is this:
Instead of giving me that message it should signal the already running process to open it's main window and refresh it's taskbar icon. You can keep a counter in the registry to check if it was previously attempted unsuccessfully and then show me the bloody error message.

[Epsilon]

They actually should change the "Steam is already running" message because that's what Steam already does.

In fact, certain features of Steam (like shortcuts to steam games, and steam:// style links) rely on the opened copy of steam.exe communicating with the version of itself that's already open, i.e. they work because what you're suggesting is already a feature.

The error message only appears when the main steam.exe has gone into a zombie state where the main loop is unresponsive, so it can't receive messages.

In other words, your two symptoms, that sometimes you get a zombie Steam process, and that you get this error message, are the same thing.