The switch supports LACP and I have verified that the trunks got configured correctly, but the overall throughput didn't exceed 114 MB/sec.
On the other end I have an Apple Xserve that also is setup to build a LACP bond - and it's unfortuanetly the only component in the puzzle, that I am not sure about. But as I said, the switch reports that there're two trunks configured and that are my Open-E box and my Xserve.
But from your reply I assume that LACP should provide a speed increase, so I will check my setup again.