Oops, we will soon have a triple-edged weapon with this Text field.
Apart from a few slight problems, ie. how to write by hand so much keywords...
but how we gonna deal with performance?
Well, Im impressed by how tags evolve during past few years. Just look at: google, delicious, devianArt, imageshack etc,etc... to see how they modeled tag collections. Im pretty sure they dont use simple text-fields for that.
Tag Clouds is the must-have feature for many websites. How you gonna track clicks without separate db ?
Of course, there is no need to put this into core, but definitely we should consider making an official plugin to handle tag collections, IMO
Perl - the only language that looks the same before and after RSA encryption.