I don't consistently see the random media block. I'm on XFMG 1.04, but also had the same problem on 1.02 prior to upgrading. The block is set to pull from a pair of categories, both of which have a decent number of images in them. I know that before moving to 1.02 I did consistently see the block, but I don't know if I stopped seeing it at the time of the upgrade to 1.02 or not, as I only noticed this past week that I wasn't seeing it (I don't generally actually look at my forum list apparently).
Ah, I see the problem looking at how the media is picked. Since my users have been piling stuff into personal albums and not the categories as of late, it is increasingly likely as time passes that the selection query will find nothing and thus display no block.
Bear in mind performance for RAND() in MySQL is incredibly poor; hopefully with it being restricted to just a few categories with a small number of images you'll be fine; but do keep an eye on performance just in case it begins to suffer. It's definitely not the solution we have implemented for those reasons, but I would expect in the short term it would be fine.
Yup. I could do better than rand() but i have a small enough set that i'm fairly certain i can accept the performance hit until the official fix is released and it was the quickest way for an acceptable bandaid. Hope the wait for 1.05 is short