It turns out that the NetworkManager service, in its great wisdom, was trying to automatically initialize the vmnet1/vmnet8 virtual interfaces created by VMware (it's using them as network injection points for the VM machines and they are managed by the vmware startup script). That means running the DHCP client over them and acquiring some garbage IP settings (these settings are supposed to be acquired by the contained VMware virtual machines, not by the physical box!). Subsequently this was installing a phoney VMware default route and DNS server entries, overriding the expected wireless settings, which in turn renders networking useless.
It seems this new behavior may have been triggered by a change in the [un]managed mode of the NetworkManager service in Ubuntu Jaunty. However, trying to change the managed=true/false statement in /etc/NetworkManager/nm-system-settings.conf yielded no results.
Luckily you can easily fix this by adding specific configuration files in /etc/NetworkManager/system-connections/ to prevent NetworkManager from touching the VMware network interfaces. You can use the following commands (assuming you kept the default interface numbering):
cat > /etc/NetworkManager/system-connections/vmnet1 << EOF
[connection]
id=vmnet1
autoconnect=false
EOF
cat > /etc/NetworkManager/system-connections/vmnet8 << EOF
[connection]
id=vmnet8
autoconnect=false
EOF
