This may or may not be of any help. I had SQL Express 2008 R2 on my PC, I had ArcSDE Personal with a few GB of data. There was an issue and I needed to get a new PC. I went and exported a full backup file (.bak) from the database that contained my geospatial data and placed it on the network.
I then went and replaced the PC, reinstalled all of the software (ESRI, service packs, SQL Express, Visual studio, etc)...once it was all squared away and working I went to the new instance of SQL Express on my new PC and restored the full back up using the same database name as the previous from the network.
I then went to ArcCatalog and reestablished the connection and all of my data and stuff was there.
Because the name of my PC changed, I had to reconnect the data in my MXDs but all in all it went pretty smooth.
If you are trying to move to a full SQL edition or to a larger SDE edition.....I would think that if you reinstalled everything in SQL as above. There has to be a way for a user to upgrade his express to standard and then upgrade sde to the full version from personal.
Regards-
Aaron