I go by plumpness of the pods and sweetness of the peas and pods.

I like to pick them when the peas inside are about ½ developed and before they get a wrinkled and silvery appearance on the pods.

" ½ developed and before they get a wrinkled and silvery appearance on the pods." Ok, follow up question -- what is 100% developed? and How do I know that tomorrow they will get wrinkled in order to pick them up today? Besides taking one off the vine everyday and eating eat, what are the current signs? Right now, some of them are sort of transparent, you can see the tiny pods inside; the others are plump and cannot see the pods but they still taste grass-like. How long does it take to get sugar taste?

Found a little info for you (from the Illinois Extension Service)

Harvesting

Garden Peas

When the pea pods are swollen (appear round) they are ready to be picked. Pick a few pods every day or two near harvest time to determine when the peas are at the proper stage for eating. Peas are of the best quality when they are fully expanded but immature, before they become hard and starchy. Peas should be picked immediately before cooking because their quality, especially sweetness (like that of sweet corn), deteriorates rapidly. The pods on the lower portion of the plant mature earliest. The last harvest (usually the third) is made about one week after the first. Pulling the entire plant for the last harvest makes picking easier.

Sugar Snap Peas

Snap peas should be harvested every 1 or 3 days, similarly to snow peas to get peak quality. Sugar snaps are at their best when the pods first start to fatten but before the seeds grow very large. At this point, the pods snap like green beans and the whole pod can be eaten. Some varieties have strings along the seams of the pod that must be removed before cooking. Sugar snaps left on the vine too long begin to develop tough fiber in the pod walls. These must then be shelled and used as other garden peas, with the fibrous pods discarded. Vining types of both sugar snap and snow peas continue to grow taller and produce peas as long as the plant stays in good health and the weather stays cool.

jollyrd, that's good info for you. You'll definitely know if you waited too long, since they'll be too fibrous/chewy. But from what you wrote, I think you may be expecting too much from them. They're called sugar snaps, but they're not going to taste sweet, like a peach or berry! And you might want to try steaming them for a short time and see if you like that. Enjoy. Dave

Like Wayne said. I like them when the peas inside are about half size.

Are you sure you have sugar snaps and not snow peas? Sugar snaps generally have a thicker pod, so they will appear plump before each pea in the pod shows definition.

Here are the peas I just picked an hour ago. The pods themselves are fleshy, crunchy and slightly sweet (with perhaps a "green" flavor). The second photo is a pod at more or less optimum size next to a pencil for scale:

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I find them sweeter when a little fatter than lantanascape's photo. I know what you mean about the grassy taste, but that is part of their charm, for those who like that. Has anyone else noticed how much sweeter the super sugar snaps are than the short vined ones? Worth the trouble of arranging something for the SShS to climb on, we have discovered.

I am so impressed with how helpful people are with pictures (like you, lantanscape). Getting pics on to the computer is still a hurdle for me, never mind getting them on garden web. One day I will practice and actually post one!

Yep, i like them probably two days past what lantanascape's picture shows. Noticeably sweeter for me. Since you're the gardener you get to decide when you like them best!

I should have mentioned that these are a little thinner than when they could be harvested, but I find that it's too easy to let them get a day or two past that perfect size, and they turn tough and lose their sweetness very quickly, so I tend to err on the side of grabbing them a little early.

Hepatica, the easiest way I've found to post photos here is to get a Photobucket.com account to upload them to. They have the formatted link with every photo, so you can just copy it from there and past it into your post here and the photo shows up. :)

Thanks, yes, everyone makes the photo posting sound pretty easy. There is just a certain tech-inertia to overcome, even to get the pics from the camera to the computer! I think I have a pre-industrial revolution soul.