Not much else to say, two examples:
1 + 2 + 3 + 4 + · · · = −1/12
1 + 1 + 1 + 1 + · · · = -1/2
This results both from Zeta regularization and Ramanujan summation. The two methods seem to me to be completely unrelated. It's an amazing coincidence so there must be a link between the two.
Another question would be: is it always true? But I'm assuming it is, or that the answer to the first question would answer this one too.