It's a good idea, too bad it's only for Android or iPhone... I'll have to continue thinking on ideas for Palm OS, Windows Mobile, Symbian, Linux mobile phones, RIM BlackBerry or JAVA phones... XD
the solution is simple, give access to your database only to people you trust and don´t access to your super important database from a public location using phpMyAdmin!
yes, me too, I have been using del.icio.us for 1+ year and now I have a gigantic un-useful tag cloud. Your app will not solve the problem of having too much tags, but at least make tags more meaningful.
I would suggest you to integrate it with del.icio.us in some way because I don't really feel like switching to another bookmarks system at this point.