Next week i'll be @ TechEd EMEA 2008 Developers in Barcelona with my colleague João Martins aka "Jota".
I hope it will be a very interesting week, Pedro Rosa from Microsoft Portugal is the owner of the dev track, and has very good sessions lined up.
So if you are going to TechEd and want to meet/talk about SharePoint contact me using the form on the blog.
When you need to do something in a list or item, in SharePoint, with a specific user you can use the SPUserToken.
Here is an example:
SPWeb webOrigUser = SPContext.Current.Web;
//get the token for the impersonation user
SPUserToken token = webOrigUser.AllUsers[USERNAME].UserToken;
SPSite site = new SPSite(SiteId/SiteUrl, token);