link packet/google dance question

I understand that it's not unusual for a site to temporarily drop or even disappear from the SERPS after using a backlink packet, but how long does that generally last? I have six sites that were all doing OK in the SERPS, with 3 to 5 keywords from each appearing on the first page. I tried using Angela's links/PJ's links to backlink three of those sites. For a few days nothing much happened. Then on December 7 all of the pages from all three of those sites dropped into SERP oblivion, and they remain there still. The sites on which I did not use the backlink packets are still showing up fine, lots of keywords on the first page of search results, so it's hard not to correlate the SERP drop with the packets.

The packet-backlinked sites are still indexed, but they're buried - pages that were on the first page of the SERPs are now number 400, 385, etc. Of course the income they had been generating has dried up. The sites are about 3 months old, and all three of them have 20+ pages of original content and already had a healthy pile of backlinks from article marketing, SB, RSS, etc. I keep reading that they'll "bounce right back" and end up with better SERP placement than ever .... I'm just wondering when. Has anyone else had the post-packet Google dance last this long?