Though polls work quite nicely the way we know them on Twitter, Facebook and Google+ (R.I.P.), there is much room for improvement.
I'd suggest some features:
1. Time limit
Polls should have an option to make them time limited, just like Twitter does it.
2. Conceal preliminary results.
If users can see where a poll is going while voting is still possible, they might change their mind.
To avoid this, polls should have an option to conceal the results until the voting phase is over.
3. Vote changes
In most social media polls, a user can chance his vote as often as he wants while voting is possible.
Openbook should offer an option to limit vote changes.
4. Conceal voters
Any poll should, by default, NOT reveal which user voted for which option.
These are my suggestions so far.
Feel free to discuss and add further options if you like.