Hmmm, I have a CF Outdoor Flood Lamp and it works fine in my photocell controlled fixture
The ones designed for that are rather new and may not be as easy to find - certainly not in all Wal-marts yet.
I switched to CFBs a couple of years ago and posted here. It's good to see the subject come up again, as they are a good idea. I doubt that they were the total reason for the $50 change in the bill, but they do indeed help. The difference per bulb can be estimated...
100 watt bulb replaced with 26 watts = 74 watts/hour saved. 74 w/h x 4 h/day x 30 days/month = 8880 watt-hours or 8.9 kwh @ 9c maybe = 80c month saved per bulb.
Okay, maybe 62 bulbs in a house could save $50 a month, or if the average burn time is more like 8 hours a month for 31 bulbs - sure.
Some of mine certainly burn more than 4 hrs/day, some hardly ever, but I have replaced some of the 2005 bulbs with the even more compact bulbs - nicer.
One mistake I made is buying some of the cheaper yellow light CFBs; I greatly prefer the bluish daylight bulbs. I don't even like the yellowish ones in closets or garage but that's where they got moved. And the prices have come down so nicely since 2005. Here's a six-pack for $15.16
Walmart.com - Always Low Prices! - GE CFL Light Bulb: 26 Watt (100W Equivalent), 6-Pk altho they do not qualify for site-to-store free shipping. $2.52 each is 10x as high as what I would pay for incandescent bulbs, but again - yeah they pay for themselves in maybe 4 months of electricity savings.