If you live between two and twenty miles from your place of work, consider cycling there.
- Time - despite many studies by the pro-cycling lobby, it will probably take you longer to cycle once you've got changed and locked your bike up. You can factor in time you've saved by not exercising separately, of course.
- Other road users - usually, other drivers are fine if you cycle defensively and predictably. Occasionally you'll encounter a moron, but that's life.
- Weather - if you have the relevant clothing, you'll be fine in a surprisingly large range of conditions. Cold rain in a headwind is rarely pleasant, though.
- Starting off - especially if you are unfit, you'll find the first couple of weeks to be really difficult. Stick with it; it does get easier.
- Initial outlay - getting all the gear together is expensive, but worthwhile. Trying to ride some old clunker in jeans and a sweatshirt will not encourage you to continue.
There are many arguments about the usefulness of helmets. I'd advise that if you're a novice and are cycling in traffic, wear one. The main argument against needing a helmet is that you rarely hit your head. This isn't the case if someone hits you unexpectedly, however, helmets aren't designed for that type of violent impact. See www.cyclehelmets.org for more.
Remember - if it's dark, or even gloomy, USE DECENT LIGHTS!!! Always carry rudimentary tools and know how to fix a puncture.