The command...

/testfor @e[type=Item] {Item:{id:minecraft:nether_star}}

...would ordinarily work, but with the new NBT tag parsing, now I get:

Data tag parsing failed: Expected '}' but got ':' at {Item:{id:minecraft:<--[HERE]

The minecraft: part IS required, since running...

/testfor @e[type=Item] {Item:{id:nether_star}}

...with a nether star item floating nearby fails with...

item.item.netherStar did not match the required data structure

The same goes for other items.

Aaaaand, unfortunately, this breaks a LOT of stuff on my map.