Where were the random controls?
From memory, all by car unless mentioned otherwise
Cesky Tesin (control leaving CZ)
Cieszyn (control entering CZ on foot at the crossing next to the castle)
Frankfurt (Oder) (entering DE, several times)
Świecko (entering PL)
Ludwigsdorf (entering DE)
Zgorzelec (entering PL on foot at Most JPII)
Kudowa-Zdrój (entering PL)
Mala Cermna (entering CZ)
Kostrzyn nad Odrą (leaving PL)
Lucni Bouda (entering/leaving CZ in Karkonosze - they moved on to the Dom Slaski afterwards)
Lysa Polana (entering SK)
And that's just the controls on the Polish borders. I've seen quite a lot of controls on other Schengen borders, including the Austrian controls at Nickelsdorf last summer where every travel document was visually checked and non-EU citizens were stopped.