Laurent, I'm also an OSS developer and somebody asked me the same thing. I must admit I couldn't be bothered with the hassle at first. However, although it took half a day to make the switch, Maven is far superior to ant and much much cleaner to work with. It's now saving the time that it cost to switch in the first place.
I would strongly recommend that you consider changing build system to Maven. The best thing to do would be to join the IRC channel and ask people to help you make the move.