As I mentioned on the mailing list earlier this month, Joshua requested a Lion buildbot from Mac OS Forge in September but I did not see a reply to that request. William, could you let us know if that is being worked on or if there are any problems about that?
lhunath, your statement "Building dwdiff fails while trying to fetch the source archive" is confused. What MacPorts trying and failing to fetch here is a pre-compiled binary, not the source code. Since no pre-compiled binaries exist for any ports for Lion at this time, next, MacPorts would have downloaded the source, and tried to build it. If that failed, then we need to see the main.log from that attempt in order to diagnose what happened. Since this ticket has now turned into a request for a Lion buildbot, please file a new ticket if you are having trouble building dwdiff.