As to swbcm's question about whether "every match" is somehow related to you, this is an explanation from another site that looks at that question...it does note that it is possible that a very short segment could be coincidental, but suggests the companies using autosomal dna testing screen those out. Each company appears to use different thresholds for determining there is enough identical segments (length, start and stop position etc are used) to report a match. This is why those testing at different companies are sometimes getting different results. This probably is one of those areas where raw data might be helpful to see if a match that ancestry.com returns is false from a dna perspective (i.e. so small it is coincidental). More likely, I suspect, is that many of these matches are outside of the genealogical timeframe, even if thru the random slicing and dicing of autosomal dna you get a big piece, it may come from somewhere too ancient to trace!
"This new type of autosomal DNA test checks about a million pairs of locations in your autosomal DNA. These locations are called single nucleotide polymorphisms (SNPs). The lab then compares your autosomal DNA with that of other customers and looks for identical segments with many common SNPs.
Often, the segments are identical because you share a common ancestor. Some short matching segments may just be coincidental. But a statistical analysis can tell the difference and predict the degree of relatedness. The more segments you share and the greater the length of those segments, the more closely related you are..."
Addendum: Jbarry has a better response to this question and greater understanding. See his posts on this thread. His last post re following-up on these dna leads is the underlying message on searching thru all of these matches