hm.... I think it's pretty unlikely that Cable is Wolverine. To start with, like FF said, Cable is taller, and his facial structure is significantly different. Add to that the fact that he has those claw marks across his face. Unless he cut himself shaving with his claws, or there's a bunch of Wolverine clones running willy-nilly in the future, I think it's safe to say that Ole Mr. Howlett did that to him. I guess it's possible Sabretooth did it to him, but Sabes has four claws instead of three, right?
And the "son" theory seems even more ludicrous to me. It's not like Wolverine was born with the claws. They were installed by Weapon X, so it's not like his son is going to inherit the claws by being Wolvie's son.
The clone theory works. But I dread that's the case.
If I were going to make a wager, I'd guess that Cable comes from some sort of future where the X-Men had a huge impact on the world, for good or bad. The comment "I've gone thirty years without a healing factor to make me better than you could ever hope to be" makes it sound like Cable consciously denied himself a healing factor. If you can just heal yourself after any sort of battle, it's going to make you a sloppy combatant. But if you have to rely fully on skill, it's going to make you that much better of a warrior. I don't think they're related, honestly. I think something very bad happened in Cable's future.... I think he got the claw marks from the future version of Wolverine. And I think he denied himself the healing factor and got the claws attached so that he can prove to Wolverine that he's better than the X-Man could ever be.
What gets me is the fact that he speaks to Jean like he personally knows her and sympathizes with her. I think, chances are, he knows her in the future, and in this future, she's realized the mistakes that Xavier (and Wolverine?) made, and disowned herself from that little family.
Either way, I think Cable's just a dude from a twisted future, who wants to prevent his future from happening, and has a hard-on for proving he's better than Wolverine.