For me a someday/maybe item is likely a project or action while a reference item may just be information. Since I don't separate my filing cabinet into reference vs someday/maybe for paper stuff I just create a folder for the item and file it in the file cabinet.
For electronic stuff if it's an action/project I usually create it in Omnifocus and set it to on-hold for someday/maybe. If it's a reference item that is electronic I create a DEVONThink Note and if necessary a folder and file it in the appropriate DEVON Think Database.
I have 7 DT databases. 1 for LambTracker and Android development, 1 for archived items from my notebook/mobile one, 1 that is archived e-mails from an earlier system, 1 I sync with my phone that contains thing I think I might need when away from my computer, 1 that is a file cabinet for electronic items, 1 that is an index of my electronic file cabinet that lives on my main computer and 1 encrypted database for all personal or sensitive information of any sort.