I've used a modified version for those budget catagories which were hard for us to control: gas, groceries, entertainment, personal, clothing. We do a lot of online billpay or auto deduction from our checking so it didn't make sense to use envelopes for electricity, cable, mortgage, phone, garbage, sewer/water. I tried the full envelope system and wasted gas driving to pay bills in cash all over our bigger city and then trying to make sure I got a receipt from the cable company (whose office was 6 miles from my house, yikes), etc.
However, using envelopest for the out-of-control catagories really helped me and DH get our spending under control and plan our activities accordingly. When the last $20 was in the gas envelope, we had to really decide about driving anything more but the absolute minimum (to work and home). Same with entertainment--when our money was out, we had to eat at home, do free activities, etc. Groceries: I budgeted $300 a month and we had to feed our family of 4 on that.
I think it is a good system but can be modified to fit a person/family's lifestyle.