Capacitive Proximity Sensing: Pluses and Minuses
Some of the advantages of capacitive proximity sensing over other sensing methods include:

1) Range of finger presence detection is fairly high (30 cm+ with an external antenna sensor and 10 cm+ without an antenna).
2) Sensitivity is higher than sensing methods like resistive or inductive.
3) Inexpensive as sensors can be constructed from different media, such as copper, external wire sensor, ITO and printed ink.
4) Minimum element size
5) Temperature stability
6) Design flexibility.
7) Resistant to environmental factors: water, temperature, humidity.
8) Works with a variety of non-conductive overlay materials like glass, with varying thicknesses.
9) High reliability and durability since they act as replacements to their mechanical counterparts.

But there are some potential drawbacks that should be considered, including:

1) The sensed element has to be conductive. This makes it work well to detect human tissue presence near it. However, it might not detect a hand approach it when the user has rubber gloves on.

2) When the conductive object remains in the vicinity of the sensor, the system could eventually recalculate its parasitic capacitance to include that induced by the hand in its vicinity. This could result in future false detects. This can however easily be remedied in software.

3) The detection range of capacitive proximity sensing decreases drastically in the presence of metal objects near the sensor. A way to overcome this issue is detailed below.

Increasing detection distance in the presence of metal objects
In the presence of metal objects, the range of capacitive proximity detection can decrease almost 15-fold. The primary reason for this is that the metal object increases the sensor stray capacitance.

Such a stray capacitance reduces the proximity response value by providing a higher full scale range. This often requires reduction in operating frequency, in turn, decreasing detection distance. The grounded metal plane also catches part of the sensor electric field and reduces the added finger capacitance.

Since most white goods have metal casings, this feature can be detrimental to such designs. However, the influence of a metal surface on a sensor is decreased by placing a shield electrode between the proximity detection sensor and the metal object, with the shield electrode having the same potential as the sensor. This is a fairly effective solution to the problem.

Conclusion
The use of Proximity sensing in consumer electronic devices has proven to add a "coolness" factor to the device apart from being functionally useful. It might be a worthwhile consideration to give your new designs a competitive edge in the market.

Viren Ranjan is an Applications Engineer at Cypress Semiconductor Corp., involved with the development and testing of Programmable System-on-Chip (PSoC)-based embedded designs, including Capsense devices and the PSoC designer IDE, which provides a setup wizard for easy routing of capacitive sensors to GPIO pins, as well as a tuner to set the threshold and noise parameters based on the specific sensor layout. He can be reached at viren.ranjan@cypress.com

References
1) Proximity Detection in the Presence of Metal Objects (AN42851) " Victor Kremin, Andriy Ryshtun, Vasyl Mandzij
2) "Capacitive sensing techniques and considerations: The basics." on Embedded.com