Like others who have replied, I love my hydration bladder and definitely wind up drinking more than my counterparts who rely on a bottle. If I want to add some electrolytes or powdered products, I will bring along a bottle as I don't like anything but plain water in my hydration bladders.
I guess I'm a weirdo... but I actually hate using hydration packs (except for trail running).
For hiking I put two regular-sized water bottles in the exterior side pockets of my pack and put a MSR dromedary inside the pack for refills. If you've never heard of the dromedary, I highly recommend looking into them. That thing is incredible, I have two and they should be beat to a pulp with how they've been treated, yet they have never leaked and are good as new... unlike every other water bladder I've experienced.
I like this method because I need to be aware of how much I have/have not had to drink. I've found that with a bladder I tend to under-drink (leading to bonking) because of a constant fear that I'll run out of water. With the bottles I can easily see how much I'm drinking and portion it out wisely (drink 2/3 on the way up, and 1/3 on the way down, etc.).
I re-use regular plastic waterbottles that I get from random stuff (I don't think I've ever purchased one, and people probably think it's weird that I keep these 25 cent bottles). These are better than something like a nalgene because you can still drink while walking. I rarely have to stop hiking to grab a swig. I especially like the Trader Joes bottle I ended up with last spring and used for a full 6 months last year, since it had a nice spout cap so I could squeeze it to easily drink on the go.
This system also prevents horrid things from happening... like a $2,500 camera drowning because a Camelback bladder decided to break four days before a four week backpacking trip to Iceland and Scotland... not that that happened or anything.
So I guess I'm crazy... but at least I can back it up with experience and reasons that mean this system works for me.
I started hiking and backpacking long before hydration bladders were available. Being a bit of a purest, it took awhile for me to even try a bladder. Now I use only a bladder when day hiking and a bladder and Nalgene bottle when backpacking.
The bladder enables me to quench my thirst without having to stop, take off my pack, and get to my water bottle. A full bladder usually sees me through most day hikes. When backpacking and I stop for a break, I will drink from my water bottle instead of the bladder so that I can possibly finish the day without having to refil the bladder. Like others, I still carry a water bottle when backpacking so that I can add flavored drink mixes to the water, which I would never do with my bladder.