I would have to say that it depend on what body you're coming from, and what you intend to use the Mk II for. As you mentioned that it would be a good body for sports, you'd be correct on that front. It is still a good general purpose body, however, and the lower resolution (as far as I know) would only be a problem if you wanted to crop the image, as it does have a lower pixel count that the T2i. If you've got the money to get the camera, I recommend that you go ahead and get it if you intend to shoot sports quite a bit. Even if you are only looking for a general purpose body, the 1D Mk II will not disappoint.
Another thing to point out (not sure if you are aware of this or not) is that the non "s" series of the 1D line (1D Mk II, 1D, 1D Mk III, 1D Mk IV) have APS-H sized sensors, which are larger than APS-C sensors and smaller than FF sensors. So the size is really in between the two. If you do decide to upgrade, you'll find that the FOV is slightly wider than it is on your T2i with the same lenses because of the larger image sensor and therefore provides some "extra" room for cropping.
As for features, the 1D Mk II does have some nice ones, such as the AF Point Expansion which is VERY handy for fast moving/action subjects. What it does is either automatically or manually (depending on what custom function you prefer) expand from the one selected AF point to the 6 points surrounding that selected AF point (for lenses less than 200mm), or the 12 AF points around the selected AF point (for lenses 200mm or longer). And besides, how can you go wrong with 45 AF points to choose from?
The biggest downside you'll notice when going from the T2I to the 1D Mk II (and this may be a deal breaker) is the screen. It's only 2" large and has a resolution of 230,000 dots/pixels. While I came from an XTi which had a 2.5" screen of the same resolution, I don't have any trouble determining whether or not an image is sharp on the 2" screen. But you may have some issues doing so coming from your fancy schmancy 3" 920,000 dot screen (if I remember correctly).
ISO performance is usable throughout the range, including 1600 with some noise reduction. ISO 3200, however, should be used sparingly as it produces quite a bit of chroma and luminance noise. It can be dealt with using the correct NR techniques/software, but the image will lose quite a bit of detail in the process. If you overexpose the image at 3200, however, you should have better results than when you use what the camera meter thinks is the correct exposure.
And here is another thing to consider: size and weight. Because of the fact that the 1D Mk II is made of a Magnesium Alloy skeleton/body (correct me if I'm wrong on the materials used) it is much much heavier than the rebel bodies, and of course, is larger as well. The weight difference (even if you have a grip on the T2i) is very noticeable. If you don't want something to big and clunky, I suggest you try before you buy and see how you like the feel of the camera in your hands. Personally I love the feel of it, but I'm still getting used to the weight aspect.
I hope this little essay was helpful (even though I'm certain that I forgot to include multiple points which I'm sure others will tell you about) and I bid you good luck on your possible upgrade. I will say this, however; once you own a 1D body, It's going to be hard to go back to anything else.