Flash and magnetic storage is different in how you want/need to handle deleted files. With magnetic storage (disks) you can (with the right equipment) read the original content of the file several generations back, not sure how many but I got a full backup out of a disk several years back (a specialist company did this for me, it cost a lot of money but they can do almost anything with magnetic storage). (For magnetic tapes the rumours said that they could get something like 9 generations of data out of it).
Flash doesn't retain the data the same way as magnetic storage, so you should probably be ok after a single overwrite or two - but read on. There's also the fact that flash doesn't like to be overwritten many times, because the cells have a limited lifetime, and thirdly, and this complicates it, whenever you rewrite a cell the device tries to use another cell in an effort to distribute the wear (in CF this is handled by the CF card itself, in SD it has to be done by the filesystem driver AFAIK). So, porting a desktop app. like e.g. 'wipe' will probably not be a good idea, it overwrites the file _many_ times (wearing out the flash), and it may not even write the same cell anyway - it's outside of its control.
I suggest you read up on flash on wikipedia, it's been a while since I did and you could probably get a better idea of what is required and what the limitations are.