To those who have a "weak" or slow last layer, here are my recommendations:
1. Make sure that your algs are optimal or at least capable of being fast. If not, replace them. My recommended plls are this guys:
http://www.youtube.com/user/jammyman3014#p/u/9/fWyjLAiEL9o. Olls are a bit more dependent on your taste, but I recommend finding algs that have little to no regrips or cube rotations if possible. Oh and try to keep them under 15 moves, 10-13 is pretty good, most will fall in this range.
2. Go through each algorithm and practice them slowly, try to find a way to do each algorithm that is fluent and involves little to no regripping of the cube. Regrips may feel quicker, but in fact each regrip takes an average of .5 seconds (if you have practiced it, more if not) and can lead to more lock ups and cube drops.
3. After you have made sure that your algs are good, begin to incorporate them into your solves. Make sure that you ALWAYS do each alg the new way you have found how to do it (regripless way hopefully) so that it becomes habit. Even if you have to stop the timer and make sure you do the correct alg, do this or else it won't stick.
4. Practice each alg hundreds of times and try some pll attacks. They may seem boring at first, but it can be like another challenge. For me at least, it eventually became kinda fun. Try to get all of your algs sub 2 at least and most of your oll can be sub 1.5 with practice. Just doing these pll and oll attacks cut a second off my time after only 1 day of practice.