FreeBSD 5.3-BETA3 is now available via FTP from sites like ftp10.freebsd.org/pub/FreeBSD/releases/i386/ISO-IMAGES/5.3/. I covered the release of BETA1 and BETA2 previously. If you'd like more information on changes to the network stack in 5.3, read Andre Oppermann's presentation (.pdf) from SUCON 04. The announcement mentions that the "MP-safe network stack is now enabled by default" and "X server configuration has been removed from sysinstall."
There is one more BETA scheduled for 10 Sep 04, followed by RC1 on 17 Sep and RC2 on 24 Sep. 5.3 RELEASE is due on 3 Oct.