Re: Very large tables

true, if you don't want to search on values too much ,or at all - use float[]. But otherwise, keep stuff in a tables as such.
It might be humongous in size, but at the end of the day - prime thing when designing a db is speed of queries.

Still, I wouldn't go too far down the 'compress and stick in as bytea' road, cos it is quite slippery, even tho might look shiny at first,
 
you can also consider vertical partition (separate machines). Honestly, I would try different approaches first, on scaled down data set, but focusing on retrieval/update (well, whatever your applications are going to use it for).