A killer-flaw in bitcoin database design?

I read this in a forum post on another site. Here's my recap. But by "I" I mean me, not the original poster.

All transactions over the bitcoin network is stored as raw data forever in the distributed database (all bitcoin clients has the same copy of the database .. and if they lose by, e.g. by reinstalling the client, they'll synchronize with the distributed one again).

You can "inject" whatever 20 byte binary strings you want into the flat files (described here http://pastebin.com/ct2WHUK5 ). I'm pretty sure there are other ways to do it as well (apparently you can add text messages to transactions?.. I don't really know).

Now, here's my question. What'd happen if the bitcoin database were flooded with virus signatures? Is this a serious matter or just a "Meh"?