No, it is not uncommon for lightening to strike aircraft. http://www.physlink.com/Education/AskExperts/ae568.cfm

Lightning striking an airplane has happened plenty of times, in fact, most pilots have had a run in with a lightning strike during their career. Can it cause damage? Yes! Does it normally cause any problems? No! Striking the fuel tanks in a way to make them explode is such a rarity that I wouldn't even consider it among the list of risks during flight. A few years ago, I was the first officer on a nighttime cargo flight. I happen to be flying this leg, but we were at cruising altitude with the auto-pilot engaged. The aircraft was a 10 yr old 747 freighter. The captain and I were in the process of completing some paperwork. It was around 4am, and I decided it was time to get my lunch. I got out of my seat to go grab my lunch box and a pop. Just as I was making my way back into the cockpit a bright flash of light illuminated the skies. It sort of went like this: Capt: Did you see that? Me: Yep, looked like a lightning flash Capt: I think it hit us. Me: Strange, any warning lights on? Capt: Nope Me: Hope my girlfriend remembered to pack a pickle with my sandwiches. Capt: Is mine still in the cooler? Me: Yeah I think so Capt: Ok, keep an eye on the systems just to be sure nothing happened, I'm going to go get my lunch too, I'm starving. --- As you see, lightning is not a huge concern for aircraft. Upon landing, I inspected the aircraft with the maintenance crew. We found a small black smudgy line across the nose of the plane, roughly 12 inches long and about 2 inches wide. Was it the lightning? Who knows!