The first time I saw it was last March I think, when it and the Shuttle came over about 30 seconds apart.
Then in mid-June I saw it go from horizon to horizon during late twilight. They have about an acre of solar panels on it now, and it is now the brightest object in the sky besides the moon.
I have yet to dig out my field glasses, but that is my plan. It's only 225 miles up
I want to see if I can make out any detail.I've seen it twice on purpose now. It's viewable between 9:30 and 11:00 pm right now, that will change as the days get shorter. It orbits every 90 minutes, so it crosses the sky in less than 4 minutes. You can't miss it if you see it, very bright, although it will wax and wane as it passes by ( the panels move to point at the sun ) as the reflectivity changes. No strobes like an aircraft.
Go here to get a schedule of viewable times for your area:
http://spaceflight.nasa.gov/realdata/si ... ted+States