The main problem I have with ~> is the change in shift key. The ~ is on the left side of the keyboard (at least my US-style keyboard), so touch typists will use the right shift key. > is on the right, thus the use of the left shift key. tchrist's "Twister" moniker comes in to play here - try typing it out a few times to see how easy/difficult it is. Maybe for hunt-and-peck typists there won't be much difference. For touch typists, we could come up with an alternative that was less discordant (such as ->>).
The fact that a quick glance at code wouldn't always tell the difference between -> and ~> is, in my opinion, both a positive and a negative. Positive in that they are so tightly related and often that's good enough, but negative in having to mentally switch gears to actually pay attention and notice it when it matters.