The "unmetered" refers to the amount of disk space you're using (combination of total file sizes and database sizes), not to the number of files. As another user pointed out in the Feedback forum, if you just go by the inode limit and the 10MB file size cap, it might appear that there's a de facto 500,000MB (slightly under 500GB) limit that you can't actually reach (since few of your files are actually likely to be 10MB). If you take your database allowance (2 DBs arranged as you wish) into account, the limit effectively vanishes into the stratosphere somewhere (50,000 inodes plus the maximum unsharded usable space in 2 databases).
If you hit your inode limit (it can happen easily if you let emails accumulate and message yourself constantly or use file writing for logging without managing the log size/extent/history), then your account will error out on just about everything - the only fix would be to remove unneeded files/directories via FTP.
But to put that into some sort of perspective, your non-DB file space allowance for a personal Free Hosting web site is approximately 4 times the total storage I had available for a major financial services company web server not too terribly long ago. (Lotsa disks, RAIDed up to here, and screaming fast - but the effective total of all of that was about 128GB.) Plus you've got the databases, which don't count against the inode count. I'm sure most people can limp along.
