This is probably WAD and may have been reported but I didn't see anything about it in the V1.1 change log or in the forum... so here it is... but it is a bit of an exploit I found... purely by accident, mostly cause no-one in thier right mind would willingly do what I did..
anyway... the maximum debt level for a civilization is -2000 credits... so there is a bit of an exploit that players can do when upgrading ships. if you select a ship class you'd like to upgrade and then click the upgrade all option you get some astronomically ridiculous number like 400,000,000 credits needed to upgrade all ships of that type...
BUT
if you go ahead and do it anyway, (like I did by accident, the first time and a few subsequent times with massive strategic value) you get the - debt of -40000000 or whatever and game over right? nope after the turn passes the default automatically defaults to -2000, so you cut all spending for a couple turns, and maybe sell a few techs to regain a positive ballance and off you go with your completely upgraded instant fleet of mega ships, and the only cost was a few turns of no production, building or reserach... which pretty small price to pay...
so really what your getting is a free 400,000,000 or so credits