Thanks for your contribution, Magnus.
One good empirical study of the motivations for, and responses to, share repurchase programs is by Grullon & Michaely and is available at http://forum.johnson.cornell.edu/faculty/michaely/the%20information%20c…. Among other conclusions, the authors find that "repurchases and dividends are motivated by similar factors. When future investment opportunities are contracting, an increase in cash payouts conveys important information about management commitment to reduce the agency costs of free cash flow when those costs are potentially more pronounced."