Can estimations be used to push the team? How?

In all teams, there are guys that are really performant, there are average and there is people that are slower (be it because of skill reasons, personal reasons or whatever). When tasks are estimated in ideal hours using a technique similar to planning poker (where everyone contributes), the result should be an estimate that falls into the average, right? To be more clear, if the task is taken by a fast member, probably it will be finished before the estimated time. If it's taken by an average, it would finish around the estimated time and if it's taken by a slower member, it will take more (probably much more) that what was estimated.

So these estimations should give us an idea of where we are in the Sprint, right? The question is: can we use them to 'push' the team? If they are used to push the team, how can it be done without hurting the sensibility of anyone and without causing people fear of taking the most difficult tasks?

These are some options:

- Asking the individual/s that hold the task why is taking so long in the standup.. This is brutal and I don't see any possible benefits (probably people will be terrified of taking the most difficult tasks very rapidly)
- Asking the whole team why certain tasks are taking longer. Much better cause there is depersonalization of the problem.
- Try to make the problem more visible. Using information radiators, everyone should be able to see the problem and pitch in to try to solve it.
- Minimize work in progress. This is another, more effective way, to make the problem visible. If no new tasks can be pulled because there is something stuck, the group as a whole will try to un-stuck it. Completely depersonalized and very effective. Wait... I am not using estimations this way :S

Ultimately, Agile relies on a group of motivated and committed individuals. If the speed at which the group is going is not enough to reach the objectives, it is a problem of all the team: managers, product owners, developers, etc. The group as a whole needs to resolve this problem. They need to figure out how to go faster. If the group shares the responsibility this way, they will find the best way to overcome it. However, there is a basic requisite that the group must hold: There should exist trust in the group. It should exist the trust that allows you to tell the group that you are stuck and need help without been judged. There should exist the trust that allows to treat the problems as problems of the team.

Comments???