This is going to seem noob like but here goes:

I have never ridden on slick tires, my new road bike came with slicks (700 X 23); my question is how do I know when its time to replace the tires?

Normally I would replace tires when the tread got really thin but now there is no tread to monitor. I just don't want to end up in the middle of nowhere with a tire falling apart.

I run mine down to the canvas. Other people use them until the tread, if any, doesn't show anymore.

Only the eccentric replace them as soon as the noodles fall off

If you get lots of gashes and cuts, especially if it's through the threads, it's time to replace.

I guess thats what I'll end up doing. There is absolutely no tread on my tires (there suppose to be that way). Also I don't feel like buying new tires all the time, I'm a lot of things but eccentric is not one of them.

Run them until you start to see the fabric or you have ill feelings toward them.
If the tires are flat prone, you'll probably replace them sooner anyway.

I don't know how long their going to last. I have about 200 miles on them with no problems at all so far I'm just wondering for the future. None of the threads I read about my tires have anything on their tire life, only that people are replacing them (stock Mondo's on a Specialized). I'll give it at least a few hundred more miles (or whatever they last for) before heading to the LBS. Thanks for the fast responses.

A lot of variables are involved, but if you ride on decent roads, keep them at good pressure, and don't skid, these should last you several thousand miles.

As the tires wear, you will notice a flatspot developing on teh center of the tire. When the flatspot gets fairly wide, it's time to replace. You'll get to know with experience what a large/small flatspot is. Some refer to the flat spot as 'tabletopping'.

When the tire is fairly warn, you'll notice that the tire flats by the smallest of debris. Carry a patch kit with you. Heck, you acn repair 6-10 flats with a kit. Would make it tough getting stranded in the mid of nowhere. I carry 2 tubes but always close to help on the trail I frequent.

Another tip is to carry a dollar bill with you. Use a $1, not a $10...I've saved myself from walking a few times when a tire has split. Use it as a boot to cover a large hole. A large hole will suck the tube right out resulting in another flat rather quickly.

Remember, a new tire can split as quickly as an old tire depending on the debris. Always carry the dolluh!

Good tires, expensive tires, new tires, cheap tires, they will all flat, be prepared.

Not a problem for me. I can't remember the last time that I actually wore out a bike tire. I always seem to get a big gash in the sidewall or something like that which ruins the tire before the tread wears out.

The back tire wears out much faster than the front. When I get a new tire, I move the old front to the back, and put the new one on the front.

Sheldon's site says - don't rotate tires to even out the wear, but it's OK to move the front to the back.

Sheldon on tire wear:

Any tread pattern other than slick serves no purpose for bikes on smooth surfaces.

Ice is smooth!

Well this changes everything.....

Easy way to check on how much rubber is left- is by the number of punctures you get. Thin rubber will allow the thorn- glass- piece of flint to penetrate to the tube easier and puncture it. Saying that I had a puncture first ride out on the new bike last year.

An easy way to check how much wear is left on the tyre is to look at the contact point on the road. Nice and round- like a new tyre and plenty of rubber left. As soon as it starts getting a "Flat" area across the tyre it is getting worn. Had a pair of race tyres a few years ago and after only 500 miles I started to see a flat area on the front tyre. Never seen that before. Checked the back tyre and the "Flat" are a was about 1 cm wide. Took the tyre off and the rubber was very thin. No sign of cord showing and no Punctures either.

You will always wear out the rear tyre first- so if you want- Buy one tyre only and put the Nearly new front tyre on the back and the new tyre on the front. Or just keep replacing the rear- or if you want to waste money- replace both tyres when one is worn- Like I do.

A treadless tire with studs would work on ice.