IDEA is a newer system than DES and 3DES, and is even more secure. Its young age means that some people prefer to use DES as a tried and tested system, but IDEA is catching on fast.
IDEA is about twice as fast as DES, since instead of 16 rounds of coding manipulation, it uses only 8. The manipulation is a mixture of XOR, Addition and Multiplication, using modular arithmetic as a basis.
IDEA is very strong, even more so than DES - once again Janne Frösen puts it eloquently:
It cannot practically be broken by brute force... an array of 1024 chips capable of a billion tests/second would be needed to find the key in a day, but there are not enough silicon atoms in the known universe to build them.
Cryptographers do like their codes to be so secure that they are technically impossible to break even if the whole world cooperated in an attempt to break them...! Unless, given more time, cryptanalysists can find another way of breaking IDEA, it is a very safe cypher system, comparable to 3DES. It is therefore used in the same areas, such as on the Internet.