ntfs3g-1.2506.ebuild been introduced 2008-05-07 ... it should be stilised by now; http://www.ntfs-3g.org/support.html#cpu100 really says we all should update. Amongst other points, it is said to use less CPU :)
Dont forget that ntfs3g-1.2531.ebuild should also be stabilised in 10 days ... and it seems to bring a lot of fixes.
It would probably be better just to wait 10 days and stabilize sys-fs/ntfs3g-1.2531 as it's not a security problem.
In the meantime, you can add something like this to /etc/portage/package.keywords if you would like to use it on a stable system: