mathx,
I just did this to my roof:
1. removed all cellulose from the floor, because I have usable attic space for storage/etc.
2. blocked all gable vents/insulated all walls. I put 1" foil faced foam (facing out), then r30 insulation, unfaced, then 1" foil faced foam (facing in). This gave me R42, and I also air sealed all gaps with great stuff (it's closed cell, and allowed me to do a little at a time).
3. DRILLED 3 3"holes in all soffit vents (the previous owner put in vented soffit over flippin' plywood, so it was more there for looks). I had this done when the house was reroofed though, so I spared myself from having to remove all the soffit to do it. The roofers just went in from the top. And at no additional cost!
a. If you vent Gable/roof like it is now, you're not giving your attic appropriate breathing in your climate. I'm in Wisconsin, which is quite a bit tamer and this was the case for me.
4. I made my own soffit vents out of 1" foil faced foam (facing up towards the roof deck) spaced 1" from the roof boards (I glued 1" scraps from the foam sheets to do this). This allowed me to maximize my r-value. You could do it with 2" foam if you're made of money. I ran these vents ALL the way up to the roof vents, then created a ceiling out of the foam/insulation method mentioned earlier.
5. I air sealed all gaps with great stuff. I spent about 250 bucks on it for the whole attic (which was over 100 cans) but it was so, so, so, so worth it.
6. I had to fur down my trusses with a 2x6 to create a larger cavity. I then filled said cavity with R30 unfaced insulation. I held it in place with drywall shims (the long, thing cardboard strips).
7. I then put one more layer of foil-faced foam, with the foil facing into my attic (to reflect hot/cold from heat/air conditioning). This covered up all the fiberglass insulation.
8. I used aluminum tape to seal all the seams on the foil-faced foam. Essentially, the insulation is air sealed from both sides, and reflective material will radiate heat out and heat/cold in, which essentially gives me a better than R42 gain.
My attic went from R-19 (and an unvented attic ladder opening) to R42/fully air sealed and properly vented. My electric/gas bill was immediately cut in half, and this month my investment has officially paid for itself (not to mention the tax break I should get in the US). It's messy, shitty work and it took me about 50-75 man hours, but in the end my attic is properly vented, air sealed, and done well all for about $1,500 out of pocket. This was for a 600-700 square foot attic space with a 6/12 pitch.