encode and decode from different number base; for example 9876543210 in base 36 would be 4jc8lii. I've learnt this from python code at http://stackoverflow.com/questions/1119722/base-62-conversion-in-python

baseXencoding

func sample_usage() {
	digits := "0123456789abcdefghijklmnopqrstuvwxyz" // base 36
	var num int64 = 9876543210

	fmt.Printf("input number is %d\n", num)
	e := encode(num, digits)
	fmt.Printf("encoded as %v\n", e)
	d := decode(e, digits)
	fmt.Printf("decoded as %v\n", d)
}

func decode(enced string, digits string) (ed int64) {
	en := []rune(enced)
	alf := []rune(digits)

	base := len(alf)
	lenen := len(en)
	var num int64

	var ilf map[rune]int64 = make(map[rune]int64)
	for k, v := range alf {
		ilf[v] = int64(k)
	}

	for i, vn := range en {
		power := lenen - (i + 1)
		num += ilf[vn] * int64(math.Pow(float64(base), float64(power)))
	}

	ed = num
	return
}

func encode(num int64, digits string) (ed string) {
	ab := []rune(digits)

	if num == 0 {
		ed = string(ab[0])
		return
	}

	var res []rune
	base := int64(len(ab))

	for num > 0 {
		rem := num % base
		num = num / base

		res = append(res, ab[rem])
	}

	res = reverseRuneSlice(res)

	ed = string(res)
	return
}

func reverseRuneSlice(slc []rune) (ed []rune) {
	l := len(slc)
	ed = make([]rune, l)
	copy(ed, slc)

	for i := 0; i < l/2; i++ {
		ed[i], ed[l-i-1] = ed[l-i-1], ed[i]
	}

	return
}

Another usage I've encountered recently is generating Natural Area Code which excludes vowels and avoids potential confusion between "0" (zero) and "O" (capital "o"), and "1" (one) and "I" (capital "i"). (http://en.wikipedia.org/wiki/Natural_Area_Code)