Horses: The only thing so far I wouldn't miss.
I'd rather see them put development time into werewolves and vampires.
I personally want this to see being worked on before 11/11/11:
- A bit better graphics, especially more advanced lighting and shaders.
- CLIMBING!
- MOUNTS!
- Sea monsters, if they aren't already in.
I didn't use the horses in Oblivion, simply because my computer isn't very good! I found it was more laggy because it had to load quicker!
However, I plan on getting a new computer by the time Skyrim is released, so I'm all for horses being in the game
I haven't noticed them in any of the footage seen though...
If horses lagged in Oblivion, could be because of sound issues with bad/old sound hardware. You could try the mod Quiet Feet MAX. Could help.
Or it could be because all creatures and NPCs were rendered horribly and lagged no matter what.