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You could probably use that or a number of similar dedicated ICs for the front end, but you're still going to need a processor of some sort to interface to the outside world, so a two-chip solution at best and you still need some front-end hardware to interface to the sensors.

I've used the very similar ADE7755 chip with success see here: http://openenergymonitor.org/emon/node/2429.  Very easy to interface and provides a higher resolution than using general purpose A/D converters in a standard µcontroller, like the Arduino or many other similar systems use. 

Using one of these chips (with the circuit adapted to provide safe isolation from the mains) makes for a very easy front end, leaving lots of processor power available for doing other things.

As Robert rightly says, it does mean a multi-chip solution, but the added complexity of this is very small in the overall scheme of things.  I always find that it's the hardware (case, connectors, front panel etc) that takes up most time, rather than the actual circuitry inside!

Overall I'm a fan of using intelligent sensors wherever possible, to simplify things in terms of code, fault finding etc.  I tend to always use one-wire temperature sensors now (DS18B20's) and what are effectively "one wire" humidity sensors, as they make life simpler.  My best find was some lovely serial output, self-calibrating, CO₂ sensors, that have made measuring and recording house environmental data very easy indeed.

JSHarris, what was the serial output self calibrating CO2 sensor you found? sounds interesting

I managed to buy a job lot of NDIR CO₂ sensors for $10 each from a US surplus store.  They are Telaire 6004 modules, that output a serial data stream with CO₂ given in PPM at 9600 baud, making them very easy to use.

I tried using the MG811 sensor, but really struggled to get it to work well enough to measure room CO₂ with any accuracy, plus it used a lot of power to run the heater.  The Telaire modules self calibrate as long as they "sniff" fresh air once a day, where they use an intelligent on-board algorithm to set the calibration with the assumption that fresh air will be around 400 ppm.

I used one of these to make a simple air quality meter/data logger for my bedroom, to sense CO₂, humidity and temperature (see here for details: http://www.picaxeforum.co.uk/showthread.php?23893-Air-quality-monitor-an... )