Bill,
I purchased boots pretty quickly after determining this was something I wanted to do regularly. The tennis shoes were not a great solution but I wasn't injured. There are issues with having adequate traction, ankle support and endurance without boots. I think that CMC also has some sort of policy that says no jeans or tennis shoes because of the issues that incorrect apparel can raise. I wan't really participating in any organized hikes so I was able to get away with it. When you are hiking with a group like that, a turned ankle or blisters or inadequate traction can imperil both yourself and other hikers so I'm sure that's why they are strict on that.
I think the trick to boots is making sure you go somewhere with a great selection and staff that knows what the heck they are talking about. Every foot and every boot is different and so it takes a lot of trial and error. I think I tried on 6-8 different pairs of boots and the ones I was most interested in I tried on more than once. The guy was infinitely patient with me. This was the locally owned outdoor shop but EMS or REI should have good staff too. If not, ask for someone else or go elsewhere. Actually nearly as important as the boots are the socks. It took me a couple of different pairs to figure out what worked well with my feet. I also needed some insoles to make the boots fit well so that was an added expense. It seems like I spent right around $200 for the boots and insoles. Like I said, investment, but I wouldn't have gone any other way. Interestingly those were not the most expensive boots I tried on that day so $$ does not equal good fit.
In terms of features, I really like having waterproof boots. Saved me on snowy hikes and creek crossing hikes. I prefer my high top for ankle support. I have Montrail boots but again, what works for me may well not work for you. I did not like Thorlo socks for my feet but have had lots of luck with alpaca wool (I think they are called Dahlgren).
One thing you might check out is Backpacker magazine at
http://www.backpacker.com. They have lots of info on how to choose and lots of reviews.
Peg
One Little Word for 2008: ADAPT