This article is from the X-Men Comic Books FAQ, by Kate the Short (firstname.lastname@example.org) with numerous contributions by others.
Two words: "Maximum Security." In that storyline, Rogue absorbed a young
Skrull girl. Because the Skrulls can change their form, Rogue's body had
a severe reaction to the absorption. Basically, when trying to find a
form to shift to, the shape-shifting power comes up with multiple
examples: all of the people that Rogue has previously absorbed.
So far, Rogue has manifested Wolverine's claws and healing factor most
often, but she has also manifested powers and features of Cyclops,
Colossus, Nightcrawler, Storm and Magneto (in UXM #388, with Colossus
and possibly Storm also in Bishop #16), and Cecilia Reyes (X-Men #108).
This also explains the red glasses in X-Treme X-Men--she's compensating
just in case Cyke's optic blasts return unexpectedly.
As for why we're seeing the claws consistently... well, Rogue wants them
(on panel) so she can be tough, and Claremont (off panel) is using her
as a substitute Wolverine. Expect to see the new powers for a while.