Bugzilla Bug 182638

gnome-extra/sensors-applet-1.7.12 has
        nvidia? ( media-video/nvidia-settings )"
However x11-drivers/nvidia-drivers-100.14.09 includes nvidia-settings (though
see bug 182622) and blocks on media-video/nvidia-settings:
        !media-video/nvidia-settings
[blocks B     ] media-video/nvidia-settings (is blocking
x11-drivers/nvidia-drivers-100.14.09)

gnome-extra/sensors-applet-1.7.12 should have
        nvidia? ( || ( >=x11-drivers/nvidia-drivers-100.14.09
                media-video/nvidia-settings ) )"

Until this is fixed, the following workaround can be used:
emerge -C nvidia-settings && echo media-video/nvidia-settings-1.0.20070302 >>
/etc/portage/profile/package.provided

I actually modified the ebuild and put it in my local overlay.
The idea is to replace the line

nvidia? ( media-video/nvidia-settings )"

with

nvidia? || ( media-video/nvidia-settings
                        >=x11-drivers/nvidia-drivers-100.14.09 )"

I think this is quite a good fix, as it leaves possibility to install
nvidia-settings as a separate package if the user uses nvidia-drivers previous
to 100* release, e.g. if the graphic card isn't supported by the new drivers.

Fixed.  Thanks.

Still fails for me with updated ebuild, I get:

# emerge -av sensors-applet
Calculating dependencies 
... done!
[ebuild  N    ] media-video/nvidia-settings-1.0.20070302  0 kB 
[ebuild  N    ] gnome-extra/sensors-applet-1.7.12  USE="hddtemp libnotify
lm_sensors nvidia -debug" 0 kB 
[blocks B     ] media-video/nvidia-settings (is blocking
x11-drivers/nvidia-drivers-100.14.09)

Total: 2 packages (2 new, 1 block), Size of downloads: 0 kB

!!! Error: The above package list contains packages which cannot be installed
!!!        at the same time on the same system.

For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

My emerge --info:
Portage 2.1.2.7 (default-linux/amd64/2007.0, gcc-4.1.2, glibc-2.5-r3,
2.6.21-gentoo-r3 x86_64)
=================================================================
System uname: 2.6.21-gentoo-r3 x86_64 AMD Athlon(tm) 64 Processor 3200+
Gentoo Base System release 1.12.9
Timestamp of tree: Mon, 25 Jun 2007 18:30:01 +0000
ccache version 2.4 [enabled]
dev-java/java-config: 1.3.7, 2.0.32
dev-lang/python:     2.4.4-r4
dev-python/pycrypto: 2.0.1-r5
dev-util/ccache:     2.4-r7
sys-apps/sandbox:    1.2.17
sys-devel/autoconf:  2.13, 2.61
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10
sys-devel/binutils:  2.16.1-r3
sys-devel/gcc-config: 1.3.16
sys-devel/libtool:   1.5.22
virtual/os-headers:  2.6.20-r2
ACCEPT_KEYWORDS="amd64"
AUTOCLEAN="yes"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-march=k8 -O2 -pipe -msse3"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config
/usr/kde/3.5/shutdown /usr/share/X11/xkb /usr/share/config"
CONFIG_PROTECT_MASK="/etc/env.d /etc/env.d/java/ /etc/gconf /etc/revdep-rebuild
/etc/splash /etc/terminfo /etc/texmf/web2c"
CXXFLAGS="-march=k8 -O2 -pipe -msse3"
DISTDIR="/usr/distfiles"
FEATURES="autoaddcvs ccache collision-protect cvs distlocks metadata-transfer
multilib-strict parallel-fetch sandbox sfperms strict"
GENTOO_MIRRORS="http://ftp.belnet.be/mirror/rsync.gentoo.org/gentoo/"
LANG="es_ES.UTF-8"
LC_ALL="es_ES.UTF-8"
LINGUAS="es en_US"
MAKEOPTS="-j2"
PKGDIR="/usr/portage/packages"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress
--force --whole-file --delete --delete-after --stats --timeout=180
--exclude=/distfiles --exclude=/local --exclude=/packages
--filter=H_**/files/digest-*"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/portage/local/layman/musicbrainz
/usr/portage/local/layman/sunrise /usr/local/portage"
SYNC="rsync://rsync.gentoo.org/gentoo-portage"
USE="3dnow 3dnowext X a52 aac acpi alsa amd64 arts asf audiofile avahi
bash-completion beagle bitmap-fonts bzip2 bzlib cairo caps cdb cdda cddb
cdparanoia cdr cli cpdflib cpudetection cracklib cross crypt cups curl daap
dbus dga divx4linux dlloader dri dts dvb dvd dvdr dvdread eds encode erandom
escreen esd evo evolution exif fam fbcon flac foomaticdb fortran ftp galago gb
gcj ggi gif gimp gimpprint glitz glut glx gnome gnome-print gphoto2 gpm
gstreamer gtk gtk2 gtkhtml hal iconv idn imagemagick imlib isdnlog ithreads
jabber java jpeg kde kdeenablefinal kdehiddenvisibility latex lcms libg++
libnotify logrotate mad madwifi midi mikmod mime mmx mmxext mng mono motif mp3
mpeg mpi mplayer mudflap musepack musicbrainz nas nautilus ncurses nethack
network nls nocardbus nptl nptlonly nvidia ogg oggvorbis openal opengl openmp
pam pcre pdf perl pic plotutils png posix ppds pppd python qt3 qt4 quicktime
readline reflection rtc ruby scanner sdl seamonkey session slang slp sockets
spell spl sse sse2 sse3 ssl startup-notification svg sysvipc tcltk tcpd tetex
theora threads tiff timidity tk totem trayicon truetype truetype-fonts
type1-fonts unicode usb v4l v4l2 vcd videos vim vorbis wma wmf xcomposite xine
xml xml2 xorg xpm xv xvid zlib" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem
bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel
intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci"
ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug file
hooks iec958 ioplug ladspa lfloat linear meter mulaw multi null plug rate route
share shm softvol" ELIBC="glibc" INPUT_DEVICES="keyboard mouse" KERNEL="linux"
LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses
text" LINGUAS="es en_US" USERLAND="GNU" VIDEO_CARDS="nvidia nv vesa fbdev vga"
Unset:  CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LDFLAGS, PORTAGE_COMPRESS,
PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS

Sorry, it is fixed, the problem is caused because nvidia-drivers >100 have been
masked, after unmasking them it works ok

Sorry for the inconvenience