I keep getting flats I have been getting flats every 20-30 miles for the last 2 months. This has caused serious inconvenience to me, as bicycle is my preferred mode of transport to work and class. Details of the situation: 


Hybrid bicycle  (Specialized Globe 2007 -- 5,000 miles ballpark on it)
Only rear wheel is flatting
Rear wheel is 622x19C rim
Tire is 700x35, Kenda 700 35-42 inner tube
I just replaced the whole rim and spokes, for $60 (I had a lot of broken spokes and the rim was out of alignment badly). However the flats keep coming.
Tire pressure suggested on the rear wheel is 30-60 PSI 
I run the pressure between 50-60 PSI
I weigh 212lbs. and I carry up to 30 extra pounds of load (backpack etc.)
The holes in the inner tube are usually single tiny punctures.
I never find anything in the tire like glass or anything
The tire seems to have been worn very quickly (it seems kind of like a cheap tire). 


Is the tire a possible cause, or is it possible that some misalignment in the hub (Shimano attached to an 8 speed cassette) is just messing things up?

This is driving me crazy... maybe I should buy a new tire and run the pressure much higher?

Run the pressure lower?   buy some specialized kind of inner tube?

I would really do anything to avoid having to patch flats every other day!

**** THANKS EVERYBODY, I BOUGHT AN ARMADILLO FROM SPECIALIZED... NO FLATS IN 2 WEEKS **** I think the pressure was way too low on the piece of crap tire i had before ... armadillo is solid!!
Are the holes always on the tread side of the tube?  Do you often go over curbs or other large bumps with the bike?  The possibilities are:


you're damaging the tube when you change/patch it
you're running over a lot of thorns/tacks
you're getting "snakebite" flats from running the pressure too low
someone has it in for you and is "helping" the tire go flat


In any event, for that much weight on a road bike 60psi is the minimum you should be running -- I run 90-100 on my 700C-35s.  You should get Kevlar-belted tires -- much more puncture resistant -- and get tires that are rated to run at least 80psi.  And I'm wondering if 35s aren't a hair wide for 19 rims -- that may be contributing to snakebite punctures.