Hello all. I hope this is the appropriate place to bring this up. I am a RoundCube user, PHP developer, and one of the co-founders of the GoPHP5 effort.
By now you have probably heard about GoPHP5. (If not, please see http://GoPHP5.org/ for more about it.) I also recall reading recently that RoundCube was considering a move to PHP 5 already.
I suppose it shouldn't come as a surprise that I would be very happy if that were true. :-) In just the few short days that GoPHP5 has been "live", we've grown to over 20 projects and over 40 supporting web hosts. The PHP development team is also considering dropping support for PHP 4 next year.
Please consider this a formal invitation for RoundCube to join GoPHP5. If you have any questions, I'll still be on the list so just ask. :-)
Cheers.