Hi, I'm new to this forum and want to ask you the "experts" whether this makes sense.  I've been browsing butterflylabs lately and noticed they have an order process to get a 600 GH/sec for $4700.  Cost aside, the catch seems to be that it will take until at least January to get the card.  I've played around with various calculators with reasonable assumptions for inputs:

Example:
instead of 600 GH/sec, I took the lower end of the +/-20% range the card specs show
I anticipated at least 5 difficulty level increases between now and then due to that fact that they seem to be going up every 10-14 days currently
I assumed perhaps $400 US for a bitcoin which is lower than today's price. 
I factored in the 350 W at high power rates 0.18 I believe

Even with all of those assumptions, the payback seems to be about a month. After that, it seems it could be a cash cow.

I don't really know whether I'd want to mine alone or in a pool as I have never done this before.  Here are a few questions I have for you guys:

-Do the mining pools take into account your contribution to the pool?  I don't want to be the one guy with the 600 GH/S card getting a fraction of the bitcoin if the 25 coins are split equally and not proportional to hash rate contribution by the individual
-Do any of you see an error in my logic for price assumption?
- Why does this pipedream seem too good to be true?  Yes, a lot of people might not want to put in 5k to get the card, but if it makes 3-4k a month, who cares?? 
-If I had a card like this, wouldn't I want to be a solo miner to capitalize on such a high tech hardware?
-Is butterfly labs a trustable company?

Is it unrealistic to think that these 600 GH/s cards will be able to find lots of coins a month and pay for itself relatively quickly and then generate income moving forward?  Or, will the overall hash rate go up so fast with everyone buying these and then the difficulty and rate of completing blocks be harder to achieve and thus I will just waste money. 

It almost seems too good to be true which is why I am hesitant. 

Thanks for the replies. I look forward to your insight.