Hello all!
I had a great ride on Sunday with my club. I went out with a faster ride than I have done before and just about managed to keep up, albeit I was working pretty much flat out for probably 50% of the 56 miles! I got a bit dropped on the hills but not too badly. There was one monster of a hill that I did suffer on - 20% gradient for near enough 500m, and I have to admit that I had to stop and put a foot down to catch my breath - only to annoyingly find that I was only about 40m from the summit anyway!
I was pretty knackered by the end of it, and my legs were still full of lactic when I commuted by bike yesterday. They weren't too bad on the way into work, but hurt pretty much constantly on the way home!
Re: queries about clipless pedals and shoes.
There are several different types of cleat and pedal systems available. SPDs are just the name of ones made by Shimano, and are aimed more at mountain biking than road. Road brands include Look, Speedplay, Time, and Shimano road. Prices range from about £30 for Shimano makes to a bargainacious £540 for Speedplay Zero Titanium Nanogram Pedals! 
The advantage of SPDs is that you can adjust the tension so that you can make them really easy to get out of. The pedals also tend to be double sided, so you don't have to worry about getting the pedal the right way up to clip in. The cleats are also quite small so you can buy mountain bike shoes with the cleats recessed into the soles. This just makes walking about in them easier.
The down sides to using SPDs is that because the surface area of them is small, you can get numbness or pressure points on the sole of your foot if you cycle for a long time. Also, as they are made of metal, they can draw the cold into your foot in the wintertime. If you use them on a road shoe rather than a mountain bike shoe they are almost impossible to walk in.
In terms of the shoe you choose, a MTB or cyclo-cross shoe will have a tread on the bottom so they are easier to walk in. The soles will be pretty rigid compared to normal shoes - my cyclo-cross shoes are just as solid in the sole as my road shoes. This is a good thing, as it helps with the transfer of power into the pedal, as flexing your foot just dissipates and wastes power. You can also end up with sore feet on a long ride. Road shoes will be slightly lighter, as they don't have a tread on the bottom. This can make walking about in them pretty precarious. They are slightly more aerodynamic.
I have SPDs on my Tricross and Speedplay on my Tarmac. The SPDs are great for commuting, as they are so easy to clip into and out of, but are quite bulky. The Speedplays were a bit on the pricy side, and were a complete bugger to set up and get working, but once I had done so I have found them to be really easy to use, and being double sided I don't have to think about having the pedal the right way up when clipping in.
For someone who has not used a clipless system before, I would recommend SPDs.