Okay, this is a serious answer.
I roller blade regularly. I also use an elliptical and I jump rope on my backyard trampoline. I've posted before.
I think of myself as a runner. I'm 47. I've been running since 4th grade. But, I'm a little older now, and I think the cross training gives me fitness in areas that running doesn't touch. When I had some physical therapy a few years ago, my therapist was shocked that I was so weak in a couple areas (I remember lateral movement with an excercise band around my knees was one of them), when I had run so many miles and seemed so fit to her.
Anyway, I believe in roller blading. I think it keeps you in pretty good shape for running. I roller blade maybe 3 times a week, jump on the trampoline once, use the elliptical once, and then I run on Saturday and Sunday each week, usually in the woods on soft, beautiful trails. I go 8 to 11 miles running. That's what I live for. The roller blading keeps my legs fresh for my running. It also keeps me healthy. If I run 6 or 7 days I week (more than 45 miles a week, I start getting injured).
I roller blade all winter (I live in a northern state, within an hour's drive of the Canada border). I can roller blade when it's all snowy in winter if the pavement is dry (snow on the grass but no ice or moisture on the road). My subdivision is 1.1 miles around--smooth asphalt. I usually do 12 laps (13.1 miles total)--six laps in each direction. It takes me about 80 minutes. I don't think roller blading is that helpful to running if you only skate for 40 minutes or something. You have to put the time in. 80 to 90 minutes is ideal for me.
I do most of it in the dark, both because of my job in the day and because I don't want my neighbors to think I'm a nut.
I jump rope on my trampoline for 80 minutes as well--the most boring kind of exercise I've ever experienced. I actually bring out a small TV unit and watch DVD's while I jump now--it passes the time. I do that in the dark as well.
Roller blade wheels last longer in the winter than they do in the summer, mostly because the pavement is cold. I get the hardest wheels I can find: 85A's or harder (higher numbers are harder). Roller Hockey wheels are usually hard and work pretty well. Also, the 80 milimeter size lasts longer than the 76 mm size--those are two of the most common sizes. A wheel larger than 80mm will not fit on my skate boots. I own two pairs of skates and usually alternte. The cost about $100 a pair. The main thing is that they are comfortable. You can't roller blade if something in the boot is rubbing your foot, giving you blisters, or poking you. Try to skate in them as much as you can in the store to test their comfort. I've bought my last 3 pairs of skates (boots) at Sports Authority. My ball bearings last about a year, or maybe slightly less. I get the best ball bearings they sell.
The worst part about roller blading is the cost of the wheels (about $40 for a set of 8 wheels is a good buy). One set of 85A hardness wheels will last me from November to March. Not as long in the warmer weather months. My skates last two years or longer.
I believe in roller blading. I think it keeps me fit for running.