Likewise the Spirit helps us in our weakness.
At Faith Community Church, we are going through Romans 8 together as a church, and this chapter is peculiarly focused on God's resources to suffer well. The choice as a Christian isn't whether or not we will suffer (for we all will), but how we will suffer. One of the resources God gives to us is his very presence in our lives, the gift of the Spirit. In the context of Romans 8, the Spirit is given to us to help us in our weakness, for we don't always know what to pray. The amazing comfort from this passage is that, though we are weak, the Spirit is strong and intercedes for us, so that God always hears our prayers, because the Spirit is interceding for us.
In life sometimes we don't know what to pray, because the issues are so complex. God's comfort is that the Spirit knows what to pray and he intercedes for us. In life the burdens can be crushing, so we don't know what to pray. God's strong comfort is that the Spirit intercedes for us.
Building off of another pastor's wisdom about prayer, I would say, the Spirit intercedes for us to such a degree that if we knew all that God knows, we would be asking the same things that the Spirit asks for us, and that the Father gives to us. This isn't a reason not to pray, of course. But it is a great reason to have hope in the midst of seasons, when we don't know how to pray. God cares so much for us, that his Spirit intercedes for us.