I did a little background piece back in the Wine School days on the difference between syrah and shiraz. Which is to say, there isn't one. Same grape. What matters is terroir, vinification, and the whims of winemakers. You may remember the basic rule: "Syrah" is the grape's name in France, where it, along with Grenache, is the backbone of many Rhone reds. French Syrah tends to be deep and earthy. "Shiraz" is the name in Australia Those wines tend to be fruitier, bolder, and less tannic. The American tradition, such as it is, is usually to tag the wine with whichever "profile" the flavor more closely resembles.
Red wines aren't alone in this multiple monickering of single grapes. Look over on the other side of the wine store, and you'll see one of the more common dual named wines -- Pinot Grigio & Pinot Gris. Now yes, I realize it's just a language difference between Italian and French -- but there's a similar process at work.
A quick aside: Pinot Gris is a "cousin" varietal to Pinot Noir. "Pinot" is French for "pine tree," which is the general shape of the tiny-berried clusters of grapes. The difference in their names stems from the color of the fruit. One is dark ("noir" is French for "black"), the other is more grayish ("gris" and "grigio" are Italian & French for "grey").
There's actually a third grape in the family, pinot blanc, but it's not grown very widely. If you see a wine labeled "pinot blanc," it can be made from Pinot Blanc, Pinot Gris, Pinot Noir fermented as a white, Auxerrois Blanc, or any blend of the four.
Anyhoo, I digress...back to pinot gris and pinot grigio. Both wines' styles are light, usually citrusy, and quite easy to drink. So easy, in fact, some of them are so light that some of the more inexpensive of either give you the experience drinking flavored, slightly alcoholic water. In general, this wine is made to be drunk young -- usually within a couple of years of bottling. The varietal has been tagged with this "don't think, just drink and work on your tan" image for quite some time. Thankfully, any number of winemakers now treat these grapes with a little more care, and versions worth taking seriously are readily available.
I can already hear you asking, "Other than the language of the grape's name, is there any real difference between the two?" The answer is yes. Italian Pinot Grigio tends to be light, have a distinct citrus character, and be very crisp. French Pinot Gris usually has a more floral nose, more mineral flavors, and usually a little more fruit and honey on the body. Versions from the rest of the world tend to follow the naming convention of the region that the flavor most resembles. For instance:
Start with Italian pinot grigio. Much of Italy's pinot grigio is grown in the Veneto, the area around Venice. I tried the Zenato 2008 Pinot Grigio della Venezie ($13) as one example. The nose is pleasantly light and peachy. It's not in the least bit watery, and certainly has some weight, with a little bit of a sugary undertone. This gets followed by more peachy flavors with an edge that tastes a little like orange peel. The finish starts soft, but eventually becomes tart, crisp, and dry.
Along those lines, if you look at an American version, you'll see many of the same characteristics. The Estancia 2008 Pinot Grigio is from California. Like its Italian counterpart, it's a citrusy, high-acid wine. Even so, it's a slightly fuller wine than the Zenato, although neither wine could be considered "heavy." Otherwise, there's a very similar flavor profile to the Italian, plus a little extra lemon on the finish.
The hub of French pinot gris production is Alsace. Alsace is famous for its dry, minerally Rieslings and Gewurztraminers. It seems like what little residual sugar is left in the country ends up in the pinot gris. These wines give you a "fuller" experience and can usually be aged a little longer than their Italian counterparts. These wines tend to be somewhat richer and more floral.
For instance, the Lucien Albrecht 2006 Cuvee Romanus Pinot Gris ($16). The nose is really "blossomy" and quite pretty. It has almost a metallic quality when initially poured, but that flavor dissipates quickly when it's had some time to breathe or been given a good swirl. What's left is a full fruity flavor. Pears and sweet apples dominate, rather than the strong citrus of the Italian versions. It still finishes reasonably crisply.
On the American side, I tried the Acrobat 2008 Oregon Pinot Gris ($12). I found a lot of the same characteristics here -- a floral nose, and a fuller body. While it is somewhat acidic, there's a lot more creaminess to this wine that you'd expect. Very nice structure and balance.
I'd really suggest that you do a pinot gris/pinot grigio side-by-side tasting, especially with summer just around the corner. Find out what you like best before the heat sets in! Also, as far as food pairings, trust the "home" regions. Pinot grigio will go well with anything light and traditionally Italian. We tried it with broiled rosemary shrimp, and it was scrumptious. As for pinot gris, it goes nicely with most of the things you'd think of with dry Rieslings and Gewurztraminers. It was very tasty with chicken and chickpea curry.