I took mine off this past weekend, and the car feels much smoother in the power band. I took off the similar filter in my wife's Toyota, and the difference was not as much as on the E90.
Emmision was not an issue when my wife's car had the check.
2006 325i Sport - SSR GT7, Euro tails, Rogue Ikon muffler/w custom 3.5" piping, Painted OEM Splitters
2005 Toyota Matrix - Commuter