*K10D and K20D are seriously sealed*
Found a Japanese web site in English that gives a bit more in-depth info on how well sealed the K20D is. Its airtight! And a quote "The K20D boasts a dependable dust-proof, water-resistant construction comparable to top-grade professional models". And its well tested to make sure of this.
Have a look if interested.
WSSA member 266PX