While using the Twin Eidolon class feature, the summoner can assume the shape of his eidolon, copying all of its evolutions, form, and abilities. Are feats also copied?
Also, can a summoner use his own feats while transformed?
The wording indicates to me that the summoner is meant to keep his own feats, but not "copy" the eidolon's feats. Specifically, that the summoner keeps his feats is supported by the idea that the rules emphasize the keeping of racial bonus feats - why keep racial feats if you don't keep other feats? Additionally, there is simply nothing indicating that you also gain the eidolon's feats. They list what you do get, and feats are not on that list.
Note: feats having to do with natural attacks, or feats that have a Strength, Dexterity, or Consitution score requirement do not get carried over in the case that the eidolon's ability scores do not meet the requirements. In fact, any feats for which the eidolon does not meet the requirements reasonably cannot be used.
Description copied from d20pfsrd.com, emphasis mine: