I haven't used them because it used to be cheaper to get them through other avenues due to the shipping charge. However, I think disneyland.com is now charging for shipping (used to be free). Still, you might check some other sites and compare with shipping to see if they're really a good deal. If you have access to a discount (teacher, military, corporate, etc), that is probably a better buy.
Personally, I don't like Will-Call. I also don't like vouchers that must be turned into tickets. I like getting my useable tickets up front. I got mine through AAA this year as part of a package. Last year we used Expedia and got the voucher-type that have to be exchanged for "real" tickets, which could be done at the front desk of the DL hotel where we stayed except that they won't do it after a certain time in the evening so we had to wait until morning and go through a long line. Now they have the kind you can print up on your computer, and as far as I know you can just go through the regular line. I think they scan it and issue you a card but I'm not sure about that.