I've found that the fthrow works against heavy characters (Bowser, DDD, Charizard) better. I can do it faster (and get better results) using z than using a shield grab, but I may be doing something wrong. Also, you can usually get at least one shock in before throwing.
If you are reaching the end of the stage, you can either go for another grab ( I like dthrow-dsmash or dthrow-nair) or you can fthrow to running upsmash, and perhaps a thunder for the finish if they di incorrectly.
Here's an example from the great Anther (right at the start of the match)
http://www.youtube.com/watch?v=OGJM0xJqajI
For lighter chars, I use the dthrow at low percents. It's really easy, just grab, shock once, dthrow, and then shield grab, and repeat, although everyone can get out of it with a footstool or just jumping (at higher percents).
Another from Anther at about 0:23 (the falling platform stopped it short)
http://www.youtube.com/watch?v=4izF4oBeha8