Well, I think anyone can see Silva's takedown defense isn't that hot, but his ground skills make up for it. Basically, if you stand with him you're dead, so you better have an amazing ground game. Even then, the Spider proved he is dangerous so go ahead, take him down and see what happens.
I think Silva's takedown defense is hindered by the fact that he tries to have his whole arsenal (Fists, elbows, knees, and feet) available at all times for his amazing standup. Unlike Liddell who can count on his hand power and spread his legs out, Silva wants all his limbs ready. That makes him easier to take to the ground, but you know, he just proved that even on the ground he's extremely dangerous.
I was super impressed with Silva. I was always hesitant to jump on his band wagon because I thought his ground skills were suspect, but when you submit Travis Lutter you prove you're bad ass on the ground.