This question comes up very often on many bicycle forums I tend to read. Now since most of these forums are dominated by a very specific breed of cyclists the answers are a little biased.
Now let's look at a person, who heard about cycling, wants to cycle and needs advice. Since bicycle culture in UK is pretty much non existant they haven't got a clue what they are doing. They've seen people going around on road bikes and now when they ask about what to buy they find out that they need carbon frame, clipless pedals (oh wait for you clipped-in moment), ultegra groupset, mitts, shoes that accomodate cleats, jerseys, helmet and an array of computers, clip on lights and bibs or gilets. Alternatively it's a fixie/hybrid/MTB.
Nobody ever says "Look, this really depends on what you want to do with your bike". If you want to race, by all means go for carbon rims and v-bars. But - if you want your bicycle to be a versatile transport think about these things
1) You don't have to wear special clothes to cycle
2) You want a bicycle that let's you carry some cargo
3) You want a bicycle that can brave the elements
4) You want a bicycle that needs hardly any maintenance
5) You want a bicycle that's durable
6) You want a bicycle that's comfortable
Now some will say that first of all you need a bike that's light and fast and that's very true - when you race. But riding in an urban environment is not about racing - I meet most people that overtake me waiting at the next set of lights. Now let me elaborate a little bit about the points above
1) I found having to change before and after the ride quite annoying. I also found out that the Dutch and Copenhageners ride in their everyday clothes. Just as you don't change to walk you shouldn't have to change for riding your bike (bar racing). It's much more convenient. Keyword: Full Chain Guard
2) After riding with a backpack I had my back all wet - not very pleasant. So I installed a rack on my racing bike to carry my work stuff with me. When I wanted to pop out to the shop to get some groceries I found that I needed a basket. In the end I ending up putting together something that didn't really belong on a racing bike, but did so because of the need for it. Think ahead. Keyword: Basket, Pannier Rack and Panniers, Front Carrier; For bigger cargo: Bakfiets, Long John
3)My racing bike did come with some puny and ineffective mudguards. They did hardly anything to stop that water from the puddles from splashing on my legs. My current bike (Pashley Princess) has beautiful full metal mudguards which are ideal for the winter weather. I go through puddles at full speed without worrying. Keyword: Full Mudguards
4) Derailleurs, exposed chain, rim brakes - the things people put on their bikes to save weight mean they have to maintain them in order for them to work. You need to clean the chain and the derailleur after every rain, lube them, adjust them, change brake pads etc. This is not something you want to do with your everyday bike - you need it to run properly with minimum maintenance. Keywords: Hub Gears, Drum Brakes, Hub Dynamo, Full Chain Guard
5)Racing bikes are made light so but that's at the expense of durability. In the end you want a bicycle to withstand the race. What happens after that is not your concern. Now with your everyday bike you need to take into account - the bicycle falling over, riding on a daily basis, weather, perhaps little collisions. Keywords: Quality Steel Frame
6) The cycling position for racing bikes is for improved power and aerodynamics. It's not meant to be comfortable. It's fun for some time, but not for long. If you don't enjoy your ride, what's the point. Keyword: Upright Riding Position.
Visit www.workcycles.com for ideas. Also I would recommend workcycles blog (bakfiets-en-meer.nl) and especially the FAQ.