How about breaking the databases up by year... ie 2000 is one set of databases, 2001 is another, etc. that way it's easier to expand in the future... you can retire old entries without just deleting them from the database.. (ie entries 3 years old are archived and taken offline or something.)
Just thinking about what will happen in four years when we have terabytes of database entries for the 200,000 lj members at that time...
Also, piman's last post reminded me of something that's been bugging me about the comment interface... read about it at that link above...