Are they good tires for commuting? Are they the size marked, or like some tires, are they a size smaller than marked? Specifically, how wide are the 35mm versions?

Searching turned up the following. The widest 700c Marathon is marked 45mm. Last post in thread:

http://www.bikeforums.net/showthread...walbe+marathon

There are a bunch of other testimonials in the forums , none of them bad. Look around there.

They are awesome commuting tires. I have a pair of marathon slicks I just mounted, plus about 2000 miles on marathon pluses. Love them both. Highly recommended.

They pretty much match the size specified, even a bit generous compared to many. I use a 28mm marathon for winter commuting and it is good on rough trails. You could go to 32mm but anything wider is really good for crossing Africa on a bad day.

I use 42mm Marathon Plus tires. One interesting thing is that the flat portion of the tread seems quite narrow compared to that of other tires. It is almost like a 32mm tread on a 42mm casing. This may be a factor in the combination of good ride and low rolling resistance. As far as mounting them, I'd say they match the size specified.

Paul

MichaelW & PaulH say it very well, to which I hardily agree. Here's what is on the Bicycle Touring 101 website. Be sure to go on to the next page as well.
Me? I've got 700 x 35c on a '93 Trek 520 tucked under fenders, and they are well worth it.