IndyGal,
There is another thread out there on carne asada, but I remember posting in it regarding cooking technique, and I don't remember if there is an actual recipe there. At any rate, it is one of my favorite things to prepare on the grill, whether to serve with rice, tortillas, or grilled veggies. The lime/orange flavor you picked up on could have been sour orange, which I know some recipes call for. If you really liked that flavor you can usually find sour oranges at your local latin market - cuban style mojo marinade is another recipe where sour oranges really add that extra zing.
But I digress, especially because my carne asada recipe doesn't use sour oranges!
You can use flank or skirt, but I prefer skirt. I don't like slicing it ahead of time for two reasons - first, it increases the surface area for the marinade to penetrate which can be a good thing, but with such a strong flavored marinade, it could overwhelm the actual beef flavor. Second, I really like the char and additional flavor imparted by grilling the meat, which you can't really do once it's sliced. I will suggest trimming/cleaning the skirt pretty thoroughly before putting it in the marinade. This is what I was recommended in the other thread on carne asada and it worked like a charm. It allows you to cook it super hot super fast to a nice medium rare and not have a lot of un rendered fat getting in your way.
Now for the marinade. There are probably endless variations out there but after a good bit of tweaking and delicious experimentation, this is mine:
1/3 cup white vinegar
1/2 cup soy sauce
2 limes juiced
1/2 cup olive oil
1 tsp salt
1 tsp black pepper
1 tsp garlic pdr
1 tsp onion pdr
1 tsp chili pdr
1 tsp dried oregano
1 tsp cumin
1 tsp paprika
1/2 cup beer
2 jalapenos sliced
3 cloves garlic sliced
That's it - put your trimmed skirt in the marinade for as long as your patiene will allow - I like a good 4-6 hours usually. Before grilling, make sure to wipe the steak clean of any bits of garlic or jalapeno as those will burn on a hot grill - not tasty in my opinion.
Hope you like it! Let us know how it turns out and if you come across any delicious modifications to this recipe, let me know cause I'd love to give it a try!