Ultimately the combination excels at creating win/win scenarios for itself, and is currently decently supported feat-wise too.
Many feats benefit the use of radiance and radiant vulnerability, but there are also several specific feats for paladin|warlocks that make the build attractive.
Crimson Legionnaire allows you to deal d10's in Warlock's Curse damage when the target is under your Divine Challenge, and Crimson Fire gives you a bonus to paladin damage against cursed foes. White Lotus feats also go a long way towards creating lose/lose scenarios for your enemy. Stat-wise, you can have a solid character with 18 Con, 16 Cha, and 12 in Int and Wis without missing out too much at all... and that's a human, who only gets one stat boost. Finally, there's Dire Radiance itself, which can potentially outdamage any other at-will in the game, since the enemy takes the full whack again if he moves towards you!
An example, then: The Paladin|Warlock opens with Divine Challenge and Warlock's Curse on a nearby foe (within 5 squares.) He then powers off Dire Radiance, dealing 1d6+4 radiant damage + 1d6 curse damage (or 1d10, if he has Crimson Legionnaire already.) Thanks to the challenge, the baddy can now try to make an attack with -2 and eat 3 radiant damage automatically... and he'd better hope he can make it without moving closer to the Paladin, or he'll eat 1d6+4 radiant again whether he attacks or not. If he DOES attack the Paladin, he'll take 4 radiant damage (if the Paladin took White Lotus Riposte already).
What you have is a character who makes a superb off-tank, but a mediocre tank. Sure, he's tough, but the nerf to the Divine Challenge means that the enemy has less incentive to attack the Pal|Warlock than his allies... assuming it can, without eating OA's or moving closer. The Pal'lock himself can deal striker damage with little personal risk, and if he DOES get attacked... well, he's got the some of the best AC around to deal with it.
Of course, if the Pal'lock can place a Divine Sanction... that's a whole different story, because the same penalties apply, with the bonus that the radiant damage from the Sanction wasn't adjusted for hybrids. You still get the original 3+CHA at 1st-10th, with increments thereafter, so that makes you just as solid a threat as a standard Chaladin (but not a Baladin with Mighty Challenge, of course.)
That's why I'M building one, anyway. And it also works thematically within the world of the campaign; the Church sanctions paladins, but some also explore forgotten knowledge in search of mysteries the gods have yet to reveal. If something whispers back, and seems to bear many of the same hallmarks as the gods (radiance, baby)... well, it's easy to get confused, isn't it?

Good plot material there, I think.
Just my two cents, anyway.