I started a directory sites few months ago, put a directory CMS on it, but never worked on it any more. Then after a while I checked the site and I saw there are thousands of pending submissions. How submitters find these newly created directories ? This is important for me because I have two PR4 and a PR5 toplist/directory, and nobody ever finds them by himself...
Sounds like you got indexed by the search engines and: 1. Either got a load of links or 2. Found via the SERPS
The directory fairy leaves them under my pillow at night. Seriously, if you ever talked about your directory in a forum it could get added to a list and shared. Most of the directories I add to my list are from a combination of forums, PM's, E-mail's, etc. Just basically people wanting to announce their directory and get some added traffic. Some people don't use directory lists and instead use search operators that will help them find directories. If your directory is indexed, chances are it can be easily found. The quality of the submissions you received may give you a clue to where the submissions came from. If they are real spammy, then thank xRumer or a similar spam software title. When in doubt, take a look at your log files. That should lead you in the right direction...
Sometimes you dont even need to submit your site to directory lists, if just a few people find your directory naturally through the search engines it filters through, they add it to their lists and then distribute and then it gets added to other lists and so on and so on.
Post in forums like digitalpoint, and submit to directory list like directorycritic. Also you can submit to my free directory list here.