The weather this year has been exceptionally mild here in northern Illinois, and I am thinking of planting my peas, green beans and lettuce in the next couple weeks. This is probably a full four weeks earlier than normal, but honestly, I don't think the ground is even frozen anymore. I am willing to accept that a serious event could kill back the plants, but would it be worthwhile to get so much extra growing season? What else might I be able to get in early this year? (I don't do tomatoes or peppers from seed usually...I buy flats of seedlings)
Peas and lettuce are very hardy and can handle a few frosts. Green beans should wait until it warms up. Other plants you might consider are spinach and kale, which are also both very hardy. (This is not an exhaustive list of good candidates for early spring planting, but I've had good experience with these.)
The challenge you will face is that seeds will germinate very slowly -- if at all -- when the soil is very cold. To get around this, you can start some lettuce plants inside and transplant them out after they're started. Most people don't transplant peas, but you can chit them: sprout them indoors wrapped in damp paper towels and then carefully plant the sprouted seeds into the ground outside.
Regarding whether it's worth the risk: the seed to plant your early crop will be relatively inexpensive (I'm guessing you aren't going to plant full packets). If you enjoy being in the garden then you wouldn't consider your time to be "wasted". If this warm weather pattern turns and you get some heavy snow you could lose the crop. I'd risk it -- not much to lose, plenty to gain!
Just be careful that you don't go out and rototill a heavy, wet soil: you could destroy your soil structure and end up with heavy clods.
I would go ahead and plant them, but if you want to be safe, you could try planting some of them now, and save the rest just in case. I do this often when I gamble with the early spring weather. Lettuce and peas can stand very cold weather, and will probably survive even if the weather turns around and gets cold. Green beans will germinate better produce a much better crop if planted in warm soil after the frost is past. Other cool season plants you could get an early start on include radishes, onions, scallions, leeks, turnips, rutabagas, spinach, most of the many kinds of salad greens, carrots, beets, potatoes, cabbage, broccoli, cauliflower, kohlrabi, and broad beans.