I can't speak for the type of chain, I still use friction, although I just recently moved up to an 8 speed (I'm not lying). As far as how often, I have a feeling your drivechain is custom fit to your chain now, and replacing the whole kit and kaboodle is in order. The chainring is the first place to look, are the teeth in the big ring looking a little like shark fins? If so, the ring is worn, and needs to be replaced if you want the drivechain to run smoothly. If you just replace the chain, shifting and all that other stuff will be a loud clunky mess. The link is supposed to be 1/2" from pin to pin. The chain will stretch under load over time, and won't fit the rings and sprockets neatly anymore, and wears them out too (the littler the sprocket, the more it is apparent). This process is faster if things are dirty. I replace my chain 2 times a year, usually in the spring, and again at the end of the season, early fall (winter is messy here, wears things quicker). I use a cheap Sram chain that costs me 9 bucks and handles 8 speed with no issues. I have found that my rings and sprockets have handled things pretty well, and I have gotten about 4 seasons so far. I am about due for a drivechain overhaul. I used to race bikes back in the 80's and put a hell of a lot more miles on my bikes then, and I think the number that stuck in my head was 3000 miles? per chain? I remember replacing my chain alot more back then. (of course I remember breaking alot more things back then too, like bikes and wheels) No science here, just what I do. If you do 150 miles a week, you might replace the chain as often as I do (I do about the same mileage). Good Luck.

(Maybe Tom Demerly can answer this one, he does own a bike shop)

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"Maybe you should just run faster..." TM

A chain should go about 1500-1800 miles, I believe. Buy a chain guage that will tell you when it's getting there. Every couple of chain replacements, you'll need a new chainring or two, and possibly a new cassette. I do a lot of riding on my 39, so it goes first.

Skipping in the gearbox can be caused by any of the three, or by stretching of your cable/rear box out of adjustment. Don't ignore it, because that noise is the sound of your gears or chain (whichever ISN'T trashed) getting ground into scrap metal.

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Cousin Elwood - Team Over-the-hill Racing
Brought to you by the good folks at Metamucil and Geritol...

What JM says is on the money. I actually broke the chain on my mountain bike(Legs of STEEL! Okay, cheap-a$$ Shimano HG chain) after less than three months. I replaced it with SMC's second best chain(PC-69) and then went through months of chain skipping. At first it was just the front middle chainring, so I replaced that with, yes, a cheap Shimano chainring, but it kept skipping, and a month later the cassette gears started skipping under load(few things in life suck worse than being feet from finally cleaning the super-hard climb inly to fail when your chain pops and your wheel loses traction.)

The moral of the story is that as much as it pained me to do so(I was in denial that a $1500 bike would come with parts that would last less than 50 hours of riding, plus I'm cheap), the solution turned out to be buying a new XT cassette and the correct RaceFace chainrings. Now the bike shifts like new, and I'm an almost happy camper. So bite the bullet, and buy a chain and rear cassette, minimum. If you find that the chainrings are showing excessive wear, you may want to consider replacing those as well.

What really bugs me is that I rode a $300 Mongoose for 8 years and replaced almost no parts. I finally bought a good mid-range bike (Giant NRS2) and have been replacing $300-$500 in parts every season.

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Now would be a good time. I go thru at least 3 a year. Don't skimp here. Get the best. IMHO, Durace since I run shimanos.