It looks like PostgreSQL Conference, US is putting on a couple of conferences in April. The first, East 2009, is at Drexel University in Philadelphia, Pennsylvania from 3 April to 5 April. The final schedule for that one can be found here.
For those on the West Coast, there is PgDay at LinuxFest Northwest in Bellingham, Washington on 25 April. Paper submissions are still being taken for that one so, if you think you want to present, check it out here.
Updates: Steve Citron-Pousty informs me (see below) that he will be presenting about PostGIS at the Bellingham conference. Additionally, Regina has informed me about PGCon 2009 in Ottawa, Canada on 21-22 May, where her group will also be talking about PostGIS.