I found out the problem was with Visual Studio trying to find
references to 3rd party binaries I was using (i.e. spreadsheet,
graphing tool) that had moved to different locations! I deleted
everything in the bin folder in the project, copied all the dll's back
in, added them back to the bin folder in the project and after the
initial build, no more delays!

Visual Studio's output was saying that it couldn't find references in
places it expected them, silly that it didn't look in the bin folder
first, but there you go! I think the problem stemmed from me adding bin
references by browsing to locations outside the project (visual studio
then copies them into the bin folder, but appears to continue looking
for the binaries outside the bin folder).

Tony.