Do you mean
MySignup.com for the second one? Yes, I've used it. It's a little clunky to get started, but works very well. My church uses it for Pumpkin Patch shifts each year (multiple 2 hour shifts all day/evening for a couple weeks - LOTS of coordination). I've used it for concession stand shifts and other things. I like the fact people can sign up and remove themselves and everyone can see exactly what shifts are open. Here's a
sample from their site. From what I recall, you can set up one basic signup for for free. But to get more features or get rid of ads or something the cost is $3. I recall the $3 being well worth it.
VolunteerSpot was actually created by somone in my town. We tried to use it this summer with Swim Team but had too many technical difficulties. To be fair 1) it wasn't ME using it, so I don't know the details and 2) start up services like this often need a bit of time to smooth out the bumps. It could be great now. It's been getting lots of local press, so I think it must work well for many.