Evolution shares some aspects of religion, and may be considered a religion depending on the definition used;
Dictionary.com defines religion as follows;
noun
1. a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects: the Christian religion; the Buddhist religion.
3. the body of persons adhering to a particular set of beliefs and practices: a world council of religions.
4. the life or state of a monk, nun, etc.: to enter religion.
5. the practice of religious beliefs; ritual observance of faith.
It sort of fits their definition, as any supernatural beliefs, or rituals and observances, are left out as prerequisites.
However the colloquial usage of the word religion is more like the definition used by the World English Dictionary;
n
1. belief in, worship of, or obedience to a supernatural power or powers considered to be divine or to have control of human destiny
2. any formal or institutionalized expression of such belief: the Christian religion
3. the attitude and feeling of one who believes in a transcendent controlling power or powers
4. chiefly RC Church the way of life determined by the vows of poverty, chastity, and obedience entered upon by monks, friars, and nuns: to enter religion
5. something of overwhelming importance to a person: football is his religion
6. archaic
a. the practice of sacred ritual observances
b. sacred rites and ceremonies
it definitely would not be considered a religion using this definition. The point in moot anyway though - note that neither definition makes the claim that a religion cannot also be based on science. The ones claiming that evolution is a religion, do so to denigrate the term that by making the claim that evolution is also a religion, then it would make just as little sense as their own religion. Its nothing more than a game of semantics. So if one would considers evolution a religion (using the dictionary.com definition), then it would still be the only religion Im aware of that is fully based on science, can be proven, and is falsifiable (as opposed to being based on any type of holy scripture).
edit - after typing that all out, I disagree with myself, even using the first definition. Evolution makes no claims concerning the cause, nature, and purpose of the universe. So no. Evolution cannot be considered a religion. At least based on these two definitions.