does profit factor ever get temporarily depleted? (e.g. you manage to make your roll to get that cruiser you've been trying to get .....does your profit factor go down for a bit to reflect the purchase or is it always @ what it is?)

It can be temporarily overstretched when failing an upkeep test (page 275). Personally, I'd offer the option of buying bonuses to acquisition rolls by temporarily or permanently sacrificing PF.

I've allowed my players the option to sacrifice profit factor to bump up a roll after they've failed to get what they need. One burnt PF point = -2 on the dice roll.

e.g. They want a cruiser but they need to roll under a 20 to get it. They roll a 34. They can choose to either fail, or to burn 7 profit factor to make the roll.

This reflects, in my mind, realistic enterprise. They are liquidating assets, burning off favours, taking loans at unfavourable rates, etc.

In my game i've also instituted a flat -5 PF when they acquire a new ship. This is a one off payment to reflect the additional burden of running an extra vessel. Of course this can soon be made up if they use the vessel wisel to increase achievement points.