I used to brew 3 gallon boils on an electric stove. Although I never actually timed it, achieving a boil took a good long time but I was able to hold a pretty vigorous boil after I got there.
Yeah, my brew kettle has some rings around the bottom from the elements I think its just the way the heat transfers. No effect on the wort that I noticed though. I never bothered to completely clean them off.
One thing to remember is you probably want to actually take it off the burner when making additions because you don't get the instant heat off with electric like you do with gas. I scorched a couple of batches a little bit when I added the extract because I left it on the burner and wasn't stirring enough.
Bottom line is it may affect your technique and timing a little, but it shouldn't have a huge effect on your final product.