"Can anybody out there advise on Bit coin's security?"
Bitcoin itself is quite possibly the most secure system in use. The security of the Bitcoin is guaranteed by node consensus (51% Majority) of the Blockchain (The public ledger). In an old post I made on HC a couple of years back, I used the phrase that Bitcoin 'Assumes 51% of the nodes are honest'. This is a bit of a simplistic explanation, as most people would point out that a majority of people aren't honest. However to elaborate, Bitcoin assumes that 51%>= of the network is not all colluding together in a massive conspiracy.
It's been beyond possibility for quite some time now for a Government or organisation to gain more than 51% power over the network, due to the sheer power of the Bitcoin network. If they were to try, they couldn't use traditional supercomputers because typical supercomputers are designed for floating point mathematics with less regard for integer (Whole number) mathematics, which is what is used in the Bitcoin cryptography. This is why miners these days buy 'Mining rigs', which are computers that are designed to work on integer mathematics quicker than other types of computers.
The fastest mining rig I think you can buy (At least from what I can see) at the moment runs at 1 Tera Hash per Second (1TH/s) called the Ant Miner S2. It costs roughly $5,000 AUD looking at the BITMAIN website. The current Bitcoin network hash rate is 720,000TH/s. So you would need to buy about 720,000 of these, power them and coordinate them to take over the network. This is well beyond any Government or organisation's capability as the fastest supercomputer in the world (The Tianhe-2) for example, only consists of 16,000 computer nodes (But is designed for Floating point ops, not integer operations).
So although the Bitcoin system itself is virtually impenetrable, the end user will always be the biggest security hole. You can easily be scammed or pillaged any number of ways, from viruses, spyware (Keylogging for example), phisphing, etc. Also, people aren't used to storing money on a computer virtually, and so as Marco pointed out, people can lose them.
I'm not too sure the last time Marco bought some Bitcoins via an exchange, so he may have more up to date information than me, but the last time I bought some I did it through Bit Trade Australia, and I thought they were pretty good. I didn't experience any problems then, but it may have changed. Unlike Marco, I bought them as a small investment, and I'm probably going to hold on to them for a long time. I have heard rumours that some Australian banks have stopped their cooperation with legitimate exchanges without cause because it threatens them, but I cannot independently verify this as I haven't done any buying in a long time (And I've never sold). It's best to ask the exchange your dealing with if there are any problems with dealing with your bank I suppose.
"I was involved with barter card in it's early days and while being a great concept also it was exploited to the hilt and barter card dollars became a joke."
I've never personally used barter card, but from what I read it is a method to barter between items directly, rather than dealing completely in currency. However, they seem to have made something called 'Barter dollars' so that there was a common denominator of price and they were fixed to $AUD. The concept of Bitcoin is completely different, it's value is based on supply/demand not fixed to anything, it's scarce and becoming more scarce (Like rare metals), but is easy to exchange and highly divisible (Like a currency).
As to another point I will highlight, you have probably heard in the MSM constant associations made between Bitcoin and criminal activity. All I can say is, if somebody really wants to use a public ledger for criminal activity, they can't be that smart. It's much less transparent to exchange in $AUD in a dark alleyway where not a sole will know.
Sorry about not replying earlier, I did see your question a while back, but it was a bit of a lengthy response. Below I've attached a video from the Australian Government review of Bitcoin. I thought it was pretty good and covered a fair bit of the basics at the beginning (Skip about 14 minutes in to where it starts):
