it is a very good workout considering that I don't have to do crunches :-D

That sounds like a good workout but I am still sore from doing one...

when I do my planking, its usually 3 sets of 90 secs with 30 secs break in between set :-)

I made to 81 seconds. How long can you go for?

I am going to see how long I can hold a plank. I am hoping to make 70 seconds. How long can you do it? A friend of mine told me that by doing the plank twice weekly (3 minutes each) he improved his 5k time by over a minute.