It appears to me that my site www.adammoss.co.uk is firmly in the sandbox for the phrase 'web 2.0 blog'. For the last 4/5 months it has been hanging around pages 2-4 on Google and then about two weeks ago shot up to page one. The next day it disappeared completely from the rankings. Does this sound like sandbox treatment to you guys? It appears on page 1, position 2 on Yahoo UK.
is it a new domain? Maybe its just settling down. How stable are your backward links? You may be being effected by temporary high quality links, i.e comments on blogs (the link appearing on the HP of the blog). Just keep link building steadily.
The domain is fairly new, about 4-5 months old. I had a high quality link on the homepage of StumbleUpon recently which caused my traffic to soar. I guess that could have had an impact.
yeh maybe, try submitting your site to various social bookmarking sites, so that you link structure varies in mediums .