From NOS: "In Velp, Gelderland [East of Amsterdam], sixty manhole covers were stolen last night. The city has marked off the holes with cones and ordered replacements. No one has been reported injured. Manhole covers are much-loved by thieves. They think the metal is worth a lot."
And sure enough, there's a whole (no pun intended) Wikipedia entry on the phenomenon.
A little back of the envelope math.
The price of iron has been *falling* for most of this year. Very generously, it looks like the thieves might get $100-$200 per metric ton for this scrap (assuming of course they have a buyer willing to take 'hot' manhole covers, no questions asked,and pay the full price). Assume the covers were made of pure iron (and not with concrete filling), and weighed 50 kg each. By my calculations, the thieves got away with 60*50 = 3000kg, or 3 tons worth of iron, so a maximum of about $600, or EUR460.
Some doubt about how many thieves would be involved: a minimum of two, I'd say, and a maximum of five.