Is it meaningful when two or more of my matches have a DNA segment or segments in the same location?

Yes. You may all share a DNA segment inherited from the same ancestor. However, you each inherited half of your DNA from each parent. [...]

If I have two matches with overlapping DNA segments, how will I know if they have those segments in common?

To tell if two or more of your matches have DNA segments in common, ask each to check for the other on their match [...]

What exactly do the centiMorgan values for DNA segments mean?

The centiMorgan (cM) values for DNA segments are measurements of how likely the segment is to recombine as it passes from parent to child. [...]

How do you determine the centiMorgan value for a DNA segment?

The Family Tree DNA bioinformatics team works with centiMorgan (cM) data from the International HapMap project.

Current knowledge of centiMorgan values across the human genome [...]

Are there limitations to the current recombination rates?

Yes. Limitations in the number of global populations used and the number of samples tested in the International HapMap recombination rate studies limit what [...]

Are the areas with extremely high and low centiMorgan values related to SNP Rich and SNP Poor areas?

No. SNP Rich and SNP Poor areas are due to the number and location of single nucleotide polymorphims (SNPs) chosen by the microarray chip [...]