Arcady's EL/CR Calculator is your friend! This incredibly useful little page takes the ECL of the various members of your party, vs. the CR of the various critters in an encounter, and calculates the difficulty and recommended experience reward. I use this at the end of every session to determine exp awards, but I also use it when building the encounters beforehand.
Long answer: Lots and lots of work by good folks in the House Rules forum-- Upper_Krust, Cheiromancer, CRGreathouse, BryonD, Anubis, myself, and others (apologies to anyone I may have forgotten).
It was Cheiromancer who coined the term "ChiRho" to denote the ratio between party Power and encounter Power (see the attached document below-- EDIT: PDF fixed).
It definitely sounds as though our DM has been using the wrong calculations for encounters for our group, which would explain why we have only had 2 encounters thus far that have made our group sweat. (Not to mention our DM's admittedly bad rolling on his side of the house against our group's great rolling, hehe!.)
I will have to share with our DM the concept of "power". Sounds quite logical and alongside the idea that the DMG's table is based on a party of 4, requires that our DM calculate the true "power" of our PC's. I can easily see how our group's CR would be 6.25, if not an outright 7 when you take our familiars into account.
And thank you for the link to the EL/CR calculator. I will forward the link to our DM.
Once again, thank you all for your input. I extend my evil DM's gratitude as well.