Something to keep in mind when living (even temporarily, but as a resident) in Spain is that Spain has a very weird system of inheritance taxes. From a political policy perspective, I'm generally in favor of inheritance taxes, since the incentives don't tend to be too disruptive (it's not like people will stop dying) and it reduces overall inequality in society by taxing what is essentially unearned income for relatives of rich people.
However, in Spain, when a husband or wife dies, any assets of the dead spouse are subject to inheritance tax by the surviving spouse. Any assets that are owned jointly, are considered owned 50% by the dead spouse and are taxed accordingly. The rates are actually quite high, which I assume means that the wealthier families in Catalunya has already figured out a way around this, but this requires structuring your assets with the help of a good lawyer. Alternatively, it's probably cheaper just to buy life insurance to cover the tax (for us for example, it's a couple hundred euros a year, which is much less than a good lawyer would charge).
Joint real-estate is also taxed, but according to its catastral (property tax) value, not the actual estimated value (which tends to be much higher, at least for now). If you have a mortgage, this gets deducted off the value.
In addition, upon the death of a joint account holder, all bank accounts are frozen until the appropriate taxes are paid. This would suggest that each partner have at least a small account only under their name with some emergency money to pay the rent, mortgage, etc.
In theory, assets worldwide are subject to this tax as well, although until now the authorities have not made much effort to track them down.
The specifics of the law are actually controlled by the region of Spain you are living in, for example, in Madrid, they've gotten rid of taxation for spouses. In Catalunya they didn't eliminate the tax, but they did lower the rate significantly in 2008 (apparently all the rich couples just registered themselves in Madrid to avoid this situation).
This is a good blog entry regarding one of the various schemes touted to save on inheritance tax.
One avoidance technique I found particularly amusing was just to lie low and wait for 5 years until the statue of limitations for paying taxes has passed.