Regarding the images, they all look very well exposed, so good job on that!
The composition in them all is great too! Overall, good work and keep on taking portraits!
I agree on the first and last parts, but without wanting to be discouraging, there's a lot of room to improve composition. Let's just take image #2. You've chosen to adapt something that at first hand looks akin to the rule of thirds. However, if you don't mind my dissection of your image, you can see below that it is actually more centre weighted.
The intersections aren't being used, and although you captured a memorable moment, it's not a very striking image. Were it to be more striking, you could have stood in front of your niece with the bird bath in between both of you and at her eye level focused on her gaze and played with the DoF. As it stands, my eye wanders without a strong focal point. You could also clone out the object popping into the top left corner.
I won't dissect the other photos of your niece, but with them all there's similarly the scope to improve composition. This is why I disagree with Sdrummer's generous praise.
As for the wedding invitation photo, I'm glad to see some of our old discussion's filtered in with a much less distracting background here. However composition and lighting fail you. How so? Well, compositionally as before, it's seemingly masquerading as a rule of third follower...but again if you inspect it closer, it doesn't. It's another centrally composed image. Not that that's bad, but it's not dynamic. The other problem is with focal points. There are 3 here: his face, her face and his shoe. Finally the smallest problem with the composition: it isn't straight - something that could be remedied with some PP. I know you've allowed me to edit your images in the past, so hoping you'll allow me again, below is a different interpretation that works a little better.
It's been straightened, and yes, it's still centrally composed because of your original framing, but what this does is eliminate that shoe and the excessive space in the background. It focuses on the two most important people concerning the invitation. The faces have been lifted with a small amount of digital fill light.
Which brings me onto lighting. One way to look at why your lighting is so is most likely because you aimed to frame the image with the bridge in the background and not around the lighting. And of course you could say that there's no way to control the direction of sunlight. Without wanting to repeat my latest entry to my blog, take a look at some of my advice on outdoor portraiture and how to control light
And lighting is where you come a cropper; it will be a factor that explains why colour in your photos aren't as good as the one by SnS that you've linked to. There just isn't enough contrast and dynamic range in your images. Image #2 has a bit more range and Sdrummer mentioned that of the 3 it looked most saturated. On my monitors they're all equal except the lighting in #2 is marginally better making it appear more saturated. Then we come to the added factor of your monitor colour calibration which may play a part in what you find in your images.
Don't be discouraged; you've made ground since I last saw your work, but there's still a lot more room for improvement.
EDIT: re: focusing issues - are you finding that the lens doesn't lock onto an object, or that the resulting photo isn't sharp? If it's on one particular lens, you might have a decentered copy, if it's all lenses, perhaps an AF issue with your 40D, if in low light, then you're probably not getting enough light for the AF module OR looking at your EXIF, I suspect that it might be DoF issues. In the wedding photo you can see that his face is less sharp than hers, and this is down to the shallow DoF at f4 with him being positioned behind her.