Do you have your collection recorded at Lugnet?
Lugnet -- LEGO Users Group NETwork -- was THE place for AFOLs to gather on the Internet back in the 1990's. Unfortunately, during a period of neglect by its owners, the online LEGO community moved elsewhere and now, today, although under new management, it's a shadow of its former self.
It has a pretty good database of LEGO sets and has better coverage of early sets than Brickset, but I am told that it isn't maintained as well as it used to be.
One feature it had long before Brickset did is the ability to record your collection on the site, and although the implementation is not as nice as Brickset's, it looks like a few people still use it. So, if you're one of them, to make it easy for you to use Brickset instead I've added a feature to enable Lugnet inventories to be imported. To do this, log in and click on the 'Import' link on the 'My Sets' page.
I've tested it using three people's inventories and it appears to work pretty well, with a 99% accuracy rate. There may be problems with sets with duplicate numbers but these, and any sets in the inventory file that are not in our database, are listed after the import. Note that importing overwrites your collection; I may make it possible to merge the two in future if there's demand.
If you give it a go, do let me know how you get on.
(Thanks to HoMa for suggesting this feature)