Hi
As it stands at the moment you can't apply the same effect to multiple clips except one clip at a time. (Willing to be shot down on this though 
)
The way around this is, once you you have finalised the editing of your Timeline, SAVE THE PROJECT.(It will enbale you to come back to it in the event you cock anything up)
Now, save your timelineas a Sequence by clicking the + sign that follows the "Sequence 1 x" This will save all the clips on the timeline as a single clip under the media list "Sequence" tab and also clear the timeline.
If you now load back the sequence onto the timeline you can apply an effect which will work on the whole of the timeline, that is to say all the clips at once.
If you want to apply different effects on different numbers of clips then you can do this as outlined above but by creating multiple Sequences of the different clips. Remember to save the project "as" with a different name each time in case of problems.
Nat