How untraceable is Bitcoin? Are Bitcoins truly untraceable or only pseudonymous to certain extents?

For example:

If somebody wants to buy Bitcoins with a Credit Card (e.g. through a third-party service) then they transfer them to a Bitcoin address. 
After that they send them to a second third-party service, which allows them to International Bank Transfer them to a fiat currency.

Can the Credit Card company or any of the third-party services trace the transactions?
Which precautions could somebody take to make the transactions more untraceable and what are the pitfalls? (e.g. coin joins, coin mixing, etc.)
Well, all transaction between Bitcoin addresses are stored forever, and so are fully traceable. What this means in your case is indeed that the credit card company can trace the coins you bought from them.

However, there are a few things to note.


Bitcoin addresses don't have a name assigned. F.e. Bitstamp will not know that the Bitcoins are coming from the credit card company because the credit card company does not have a list with all the addresses they use. An exception would be when you used a green address. This also holds in the opposite way that the credit card company does not know you funded Bitstamp with the coins since they don't know that the address you sent the coins to is owned by Bitstamp.
Bitcoins can move around very fast. When your coins end up somewhere the credit card company can link some person to, it is very likely that they are not spend by you anymore. With as few as 2 hops, the coins could have gone through an exchange and ended up by a totally different person.
The Bitcoin change system gives you better privacy as well. When you only spend a part of the Bitcoins in an address, by default, the change - which is the part that is not spent - is send to a new address. So, when you are spending some coins at different places, the coins you still have yourself also made several hops, so it is hard to tell if they are still in your possession.


Then, when you really want to make sure people cannot trace transactions back to you, you could use Bitcoin laundry systems. These are services that take your coins, shuffle them around among many different addresses they own, and let you receive the coins - minus the commission they take - back at another address for you. When you use a sophisticated Bitcoin laundry service, it is practically impossible to trace your coins. But beware, when dealing with very large amounts of bitcoins, this will be harder to achieve. Consider laundring your coins in smaller chunks.