The original Street Fighter 4 will not go quietly into the night. Posted on IRC just a day or two ago is a handful of ways to set up unblockable Ultras with Sagat, Seth, Rose and Ken. The original video was taken from NicoVideo but since then many more videos have shown up giving players a look at how this works. The basic idea is there is a short time during the Ultra freeze where the character cannot block. By sending a projectile their way that hits them in this short period of time allow these characters to follow up with an Ultra.
The big questions is, will this still be possible in Super Street Fighter 4? If so, it could change the landscape of the game dramatically for those with a projectile, but at the same time it's been reported that most of these are pretty hard to do with any sort of consistency.
Here is an example with Sagat, and you can check out the full thread on SRK for all the nitty gritty details.
Source: #capcom, SRK