The WD-40 is very popular in the UK. Use it to spray your rod rings, hooks, lures and trebles, etc to prevent corrosion. However,
do not spray WD-40 in your reels as it will remove grease. Rather ensure that your reels are properly greased and wash them (rinse not dunk!) with fresh water after use, and use a proper reel oil to lubricate and protect. You can use WD-40 to remove all the old grease when servicing your reels.
Many anglers believe that the WD-40 actually services as an attractant when sprayed on bait and lures. Of course there is a lot of skeptisism on this matter! Check out the Yahoo topic:
Has anyone used WD40 as a Fish Attractant?
Edit: Apologies for going off topic on this really good thread, I should probably post it in the original
Tackle care thread.