Nice writeup, and a neat project. Years ago I made a similar LED light with a series string of LED's. A bit different in that I ran more in series, and where I am at the mains AC came in the 120V 60hz flavor. I found that I did not use adequate protection from voltage spikes, and, since diodes often fail to short, it didn't work out so good, I wound up with lots of fried led's.
If you compare Lumens per Watt, you may find that the LED's you are using perform worse than compact flourescents which are at about 60 Lumens per Watt overall. Cree and some other manufacturers are currently producing and selling LED's that top out at 100 Lumens per Watt, which compares with the best Flourescents. Small LED's are generally good where directional lighting is needed, such as reading lights, under cabinet or task lighting, but the overall efficiency of most 5mm LED's I have seen is generally under 35 Lumens per Watt. Ghurd from here has more knowlege on what is available in these types of LED's though. Most lighting projects that I have built recently utilize the high efficiency Cree LED's for this reason.
More recent efforts powered from mains have involved high efficiency switching power supplies to take the voltage to around the voltage needed to drive the current for a series string of three or less, and a small value current limit resistor.
If you search the board there is a highly robust DC driver circuit developed by user 'Commanda', who is much more knowlegable than I about electronics, which I borrowed for some high efficiency LED lights which used for a remote overseas project that I helped out with BTHumble from the board here. Here was the writeup of that project: http://www.fieldlines.com/story/2008/3/14/55046/0695 The prototype of that light which I built is still in regular use at my house and is functioning well. As of the last report, the lights of this type that we installed in Fiji were all still functioning properly. If the LED's performed as rated, as I did not attempt to measure the light output, and the current and voltage measurements I took were accurate, those came in at about 60 Lumens per Watt under normal operation. While not better than compact flourescents, they are likely much more robust, but time will tell.
The more recent DC power lights I have made for my own use here have used a PWM driver made from a simple low power version of the 555 timer chip. They are a bit more power efficient over the voltage swings of the battery banks, but they are probably not as robust as Commanda's driver circuit.
The advances in LED's have been exciting. As you have noted, the trick is to get the power through the LED's while wasting as little of it as possible within the driver circuit, or LED for that matter, which turns up as heat.
