Before Swiss-cheesing, please read the following paper:
http://www.chiefdelphi.com/media/papers/2220
That being said, "lightening" holes are not a bad idea, just plan them out. Last night we swiss-cheesed a set of components. to give you an idea of the effort, 48 1" holes through 1/8" aluminum was worth about 0.48 lbs This took a significant amount of time and made a huge mess, and as far as i know, that kid is still deburring the parts...
1" hole = (.5^2)*pi = 0.785 in^2
x1/8" thick = 0.1 in^3
Aluminum is 0.1 lbs/in^3
thus each hole is 0.1*0.1=.01 lbs
x 48 holes = 0.48 lbs.
Note that larger holes do have more area, but you can make fewer of them. a 1.5" hole would remove (1.5)^2 material or 2.25 times as much material, but you can only drill 2/3 as many holes. Thus for the components we were looking at, we could do 48 1" holes, or 32 1.5" holes. The 1.5" holes would have been worth 0.8 lbs (.28*2.25*(32/48), but would have reduced the structural integrity of the component too much. this exercise took 10 minutes to do and saved us from scrapping components that had 10+ man-hours in making.
Please drill responsibly!
