Gentoo users are expected to be proficient with the command line, but that doesn't mean it is always the best solution. Just as thousands of Debian users browse the available or installed packages, and even install updates, using the Synaptic GUI front end to apt without the World coming to an end, so Gentoo users have had a choice of graphical interfaces too. The main difference is that the Gentoo options have been rather poor, especially when compared with Synaptic and its usability.
Himerge is an attempt to redress this by providing a Portage front end written in the Haskell language (which is reflected in the name). Himerge goes a stage further and not only allows you to sync your portage tree at the touch of a button, browse the available packages, install and uninstall packages and all the others things you can do with Portage's emerge command, it also incorporates the function of some other useful Portage utilities, like eix and equery.
USE flag browsing and editing is supported, both globally and per package, and Himerge uses eix for fast searching of the available and installed packages. You will never replace the need for the command line in Gentoo, nor the desire of Gentoo users to use it, but a graphical client is sometimes the better option, and this is a good implementation.
You'll never pry most Gentoo users away from the command line permanently, but this is a useful addition to the system