When updating your system or installing a new program you run into "blockers". Blockers in Gentoo ebuilds simply mean that two packages cannot be installed at the same time in the same system.
When upgrading, these are usually packages that have been superceded by other packages. And this is unfortunately common with too generic names for libraries, such as libnw that is either dev-games/libnw or sci-biology/newick-utils.
[blocks B ] app-mobilephone/obex-data-server ("app-mobilephone/obex-data-server" is blocking app-mobilephone/obexd-0.43-r1) [blocks B ] app-mobilephone/obexd[server] ("app-mobilephone/obexd[server]" is blocking app-mobilephone/obex-data-server-0.4.5) * Error: The above package list contains packages which cannot be * installed at the same time on the same system. (app-mobilephone/obex-data-server-0.4.5::gentoo, ebuild scheduled for merge) pulled in by >=app-mobilephone/obex-data-server-0.4.5 required by (gnome-base/gvfs-1.10.1::gentoo, ebuild scheduled for merge) (app-mobilephone/obexd-0.43-r1::gentoo, ebuild scheduled for merge) pulled in by app-mobilephone/obexd required by (net-wireless/gnome-bluetooth-3.2.1::gentoo, ebuild scheduled for merge)
Removing the blocker in this case is as simple as removing the "server" USE flag.