Update:
We received our first post-LED installation electric bill yesterday, and compared to last year it was substantially lower, even though we've been colder than last year, and we have 35 days on this bill compared to 30 days last year. Using last years amount and extending it the extra 5 days I would have expected our bill to be just over $100, but the bill was only $81. The new LED bulbs were in use for 18 of the 35 days of the billing cycle.
A very rough estimate is that the bulbs saved us about $1.20/day during their use this billing cycle. Keep in mind that we're in the winter months and we operate lights much more than we will in summer. We've also had 2 gatherings at the house where many lights were on for a long time. We had two similar gatherings last year about this same time.
I don't expect to see that much of a savings over the summer months. But even if the savings average 90 cents/day year round, that's over $300/year in savings, and is on track for a 3 year payback which about what I had originally estimated.
Again, these are just rough numbers and I'll have a better handle on them after our next billing cycle when the LED bulbs will have been in for the full cycle. Our electric rates are about 8 cents/kWh.
So far I'm very happy with the bulbs themselves. There have been no failures, no buzzing, no flickering, etc. It's also nice knowing that when I turn on all the lights in a room they're using less electricity than one or two of the single incandescent bulbs.