If you know which airline you will be flying and our concerned which seat you will land up with as last time you flew you were seated near the toilets and couldnt get any sleep with passengers standing on your head all the time or want to sit near the food pantry so that next time airline decides to run out of vegetarian meals on board you were one of them few lucky one served. Everytime we meet a traveller he/she does have a story to share on how they could have been better of if they knew which seat they would be getting and where its in the plane.
Now this site cant say if it can help with ensuring a seat but atleast telling you about plane you are going to fly and which seat is where with its good and bad. This let you pre-determine which seat you will request when you reach the airline counter at airport. As they cover singapore airlines its been a big help especially i know which plane they fly on Delhi-Singapore route.
Go check out seatguru.com