Now that's a catchy headline !

> Whose image would be more tainted, the victim's or the attacker's? Imagine the headlines: "US government spends millions to hack and steal digital money from US citizens and foreigners".

All it takes is a few key people in the governement starting to think BitCoin is somehow "bad for the US dollar" and then they will find some official or non-official agency to take care of it.
After all, governement secret agencies of all the countries around the world are known to do much worse than hacking a network...
And there will be no bad press. When caught, they'll just say: "we terminated a network of internet hackers designed to undermine the US currency", or something along that line.

To avoid this scenario, I can think of 2 things to do:
1- Continue to make clear that BitCoin is good for everyone (including governements), not a way to avoid taxation or screw governements.
2- More miners, so that BitCoin is more resistant to attacks.

It is very possible that I overestimated the problem.

However I was talking about some entity willing to shut down BitBoin, not making a profit from it.
In that case, the double spending problem would be used to undermine the trust in the system, not getting rich.
If an attacker is able to create long alternative branches, it would be able to revert many transactions and double spend money. If the attacker is able to do it for an extended period of time (say, a few months) then the trust in the system will be pretty much distroyed forever.

> I agree the number of miners need to grow, but the good news is, with today's rally, it is going to grow fast

It's great the number of miner is growing fast
However, I think you need to encourage new miners to mine.
Another thread on this forum is talking about removing the "Generate bitcoin" feature from the base client. Based on the reasonning above, I think the network needs more miners, not less.
Perhaps that instead of mining alone, the base client could join some kind of default/official pool so as to encourage participation and collect a few bitcoin ?

I think the bitcoin mining power needs to keep growing rapidly for the years to come.

Here is why I think so:
In theory, to successfully "take over" the bitcoin network, one would need to have more processing power than all the other miners combined.
Right now, how much would it cost to achieve this ?
For a total network hashing power of 600Ghash/s, with a GPU able to do about 300Mhash/s (Radeon 6950) costing about $250, it would cost 600,000 / 300 * 250 = $500,000.
This amount is for the GPUs alone. Obviouly one needs to add other components (motherboards, power supplies, ect), then one needs to pay some heavy electricity bills and probably hire a team to build that big GPU cluster.
Ok, let's say, this would double or triple the price.
In the end, we are talking about 1 or 2 millions dollars here.

For an individual, this is rather difficult to achieve.
But, if any governement or big corporation on the planet felt threatened by the bitcoin economy and wanted to shut it down, it could do so relatively easily.
A few million dollars is not much money for them.

Remember that governement have shown willingness to shut down alternative currencies in the past (liberty dollar, eGold, eBullion). BitCoin is different from those currencies, but at some point someone may consider it as a threat.
To make those big players think twice about shelling out money to sink BitCoin, the cost would need to be at least $100 million: a hundred times higher than it is today.
In the long run if BitCoin goes global, the costs would need to be even higher by several orders of magnitude.

So, what I suggest is:
1- keep increasing the mining power fast. Find new way to make people and business participate in mining.
2- be careful not to piss off anyone too much. especially not governements and some 3 letters agencies

HTH !
Note: sorry if my english is not so good, I lack pratice