This is the first year I expect to pick any of it. I planted it last year, and thought it had better get established before I started picking, although it grew quickly and well. I'm not sure whether I have French or Garden sorrel since I grew mine from a packet a friend gave me - which was labelled in Russian! They are two quite similar species, rumex scutatus (French sorrel) and rumex acetosa. French sorrel may be little the more tender and mild of the two, but they can be used interchangeably.
While sorrel is easily found as seed or young plants for the garden, it seems strangely absent from groceries and markets. I hope it can be found in some farmers markets, but at any rate anyone with even a small garden not necessarily dedicated to growing vegetables can grow sorrel. It has a lot of relatives, many of which are highly successful weeds (rumex acetosella, grrrrrrr!) and it retains a weed-like robustness and tolerance for different soils that makes it an easy plant to grow. However, unlike its more weedy relatives, it doesn't spread by runners but stays in a nice clump. I would recommend removing the flowering tops before they go to seed though, or it will be everywhere. It's also a relative of spinach, rhubarb and buckwheat. The leaves are rather spinach-like, with a tart lemony flavour reminscent of rhubarb, although not that sour.
Tender young leaves can be added to salads, made into sauces for eggs, fish, or chicken, put in soups and used to liven up the last of the previous years potatoes.
It's generally regarded as best in the spring, because the leaves are most tender and mild when grown in cool, moist weather. However, fresh young leaves could be used throughout the summer if you really wanted to. Perhaps a better plan is to give them a rest during the hot days of summer, then start picking again in the fall when things cool off.
If you don't have an herb or perennial vegetable bed in which to plant sorrel, it could go into a perennial flower bed quite easily. The leaves are a mid-green arrow shape, a bit coarse but not unattractive, and a small patch would make a good neutral background to more showy plants. A spot a foot around would be sufficient, although if you like it you will want more than that. Along with Welsh onions or walking onions**, sorrel is an exciting find in early spring when we are longing for fresh green things from the garden and worth finding space for, in even a very small garden.
* I wrote this a couple of days before I wandered out with my camera, planning to photograph the patch (which I did. See: photo) and pick some (which I didn't. See: photo). It was the first thing picked, all right. The deer picked it. Those bastards. I thought they weren't getting in any more. I thought we had an agreement: they wouldn't eat my veggies, and I wouldn't eat them. So much for that.
** Seen in the photo next to the sorrel. Apparently the deer don't care for them. Hu-bloody-rray.