I have done exactly what you're describing and so have many others. Current transformers are extremely easy to install and safe, provided you simply turn off the power when you install them. They are low voltage so getting the wires out of the mains box is easy. And, then, this is almost the only place you deal with wall level power.
Personally, I put the current transformers in myself while the box was live (you don't have to disconnect anything) and it took about 15 minutes from walking up to the box to walking away with the wires already run inside the house where I put the electronics. I used a wishield, which isn't produced anymore and later switched it to an XBee and did the web interface on another Arduino inside my house. My mains box is on the side of the garage about 50 feet from the Arduino that interfaces with the web.
I used a wall wart to power the arduino and have another step down transformer to measure the mains voltage. I have the project posted and the code I am running to measure the power. There is also a link there to other folk that are doing similar things at an open energy project in Wales. They have created a library for the Arduino IDE that does most of the work for you. I don't currently use the library because it didn't exist when I started the project and why fix something that is working?
How easy it is to do depends on your skill level and interest. It took me a month or so to get the various parts and have a prototype running on my kitchen table. I split an extension cord and put the current transformers on it to test. I used a toaster (1500 watt) to create a load I could turn on and off for measuring power; comparing the various readings to a kill-a-watt I picked up at Home Depot.
So, what amperage drop do you have to your house? Mine is 400 watts, split in the box to two 200 watt feeds and I am only using one of them currently. It was the biggest drop I could get in a residential area and I didn't want to come back in a few years and have to upgrade. This number will determine which current transformer you need.
Of course, this got me started on handling devices around the house. Originally, I simply showed the power level on a web page. Then, I wanted to be able to see it any time so I made a display that would show the power and mounted it on a wall. Then I wanted to record it over time so I put in an interface to Pachube. Then I ........ Needless to say, I'm still working on it and incorporating lots of things around the house. I even went so far as to replace the heat pump thermostats in the house with arduinos and have full control of my heat and A/C over a web interface. Once I could measure the power and see what was actually going on, I installed a solar hot water heater for the house water, solar heater for the swimming pool, inside and outside temperature sensors.
The code, hardware and techniques are all documented on my blog at http://draythomp.blogspot.com/, the tabs at the top link to the various projects. It isn't hard, it isn't any more dangerous than any other project around the house and it's a heck of a lot of fun. Currently, I'm saving over U$100 bucks a month in power bills, but I use electricity for everything here in the desert.