Hi Christian, Thanks for your email!
Only in late July this year I did again observe severe occurences of this phenomenon and was starting a conversation with Philip Smith (Cisco) and others.
Could you elaborate on the phenonmeon you observed? In particular, how were you able to determine it was caused by the BGP convergence effects? As described in Randy's talk (http://www.ripe.net/ripe/meetings/archive/ripe-43/presentations/ripe43-routi...) we are currently using "BGP Beacons" (an unused prefix that is announced and withdrawn at well-known times) to improve our understanding of the BGP dynamics, and hopefully use that as a calibration mechanism to understand the causes of BGP updates. We hope that someone in Europe could also help out with the experiment, details of which are described at http://www.psg.com/~zmao We currently have two beacons in the U.S., some topology diversity would really help. Thanks! --Morley