I'd like to add a couple of things about RCO lag as it relates to Pikachu and in general:
As has already been stated, RCO lag is extra frames that will apply the lag you would've had with QA to your next landing. Pikachu has way more tools than pretty much any other character to deal with this though, since QA is so versatile. The most annoying thing about it is if you get hit out of your QA and are forced to land unexpectedly, your opponent can get a medium to heavy punish from it (I actually found a PERFECT example of this. Even though Nike messes up a turn around, it still shows exactly how it can happen
http://www.youtube.com/watch?v=CXrS_QOHNU0 @ 0:32). Just be careful.
Another interesting point about RCO is that if you land with an aerial, you'll get what I *believe* is the normal landing lag of that move plus another 1/3. This is why Marth's will come back on stage with a nair or uair after up-bing to the ledge, since they have very low landing lag already.
I could probably add more, but I'll end with noting that RCO lag is the reason why we can really destroy Marth with t-jolts on the ledge. He simply doesn't have safe options to deal with it, and will be forced to eventually choose a really committing option to regain stage control.