Jim Dunlop Shell, Heavy (that's probably 1.0mm). Celluloid, sounds beautiful on acoustics.
i think there's a diff in the sound. It is especially apparent when playing acoustic guitars. Soft picks are good for strumming (esp. fast ones) but not for solos as softer picks cannot generate as much volume; and the notes sound weak. A lot of ppl use thicker picks as it's more versatile and with the proper technique, strumming with thick picks will sound as good as using soft ones. The difference is probably less obvious when playing distorted...
Just my 2 cents worth. Haven't been playing electric for a while now; on a classical diet. fingers!... Cheers! =)