The market analysts at comScore this week released their latest US smart phone usage share survey, noting that Microsoft's Windows Phone was in use on just 5.8 percent of smart phones in the second quarter of 2011. That's down 1.7 percentage points from its 7.5 percent figure in the first quarter of 2011.

The top smart phone platforms in the US, in order, were:

Google Android - 40.1 percent (up 5.4 percentage points quarter over quarter)
Apple iPhone - 26.6 percent (up 1.1)
RIM Blackberry - 23.4 percent (down 3.7)
Microsoft Windows Phone - 7.5 percent (down 1.7)
Nokia Symbian - 2.0 percent (down 0.3)

The top hardware makers in the US, in order, were:

Samsung - 25.3 percent (up 0.8 percentage points)
LG - 21.3 percent (up 0.4)
Motorola - 14.5 percent (down 1.3)
Apple - 8.9 percent (up 1.0)
RIM - 7.9 percent (down 0.5)

(I'm intrigued that both Samsung and LG phones were in use by over twice as many people in in the US in both Q1 and Q2 than were Apple iPhones.)

But back to Microsoft. Those Windows Phone numbers do of course also include Windows Mobile devices, since comScore is measuring usage here, not sales. (New Windows Phone sales are all Windows Phone 7 handsets, not the older OS.) So the declining usage share in the US suggests that Windows Phone devices are selling slowly (which we knew) and not picking up the slack as customers move off of Windows Mobile (which is a bad sign).

Of course, a new generation of Windows Phones, powered by Windows Phone 7.5 ("Mango") may help. I hope so: Windows Phone is such a great smart phone platform, and it's pretty clear that most people don't even know it exists.