are these things getting popular i notice cabelas has a page or 2 of them and whats the  diff in a centerpin and a flyreel???

From a Fishonbc article (Steelhead site):

Center Pin reels come in many styles and from many different manufactures. These reels can cost any where from about $250.00 to over $600.00 dollars depending on the model. When choosing a reel you must first decide where your budget is, as these reels are expensive. Center pins are all very similar they are a very simple design basically what we have here is a large fly reel with the ability to free spool line so we can cast and make drifts while fishing. Some center pin reels are equipped with bearings and some have a bushing drive. Bearing models are the most widely produced at present as they spin faster and longer right out of the box, however do not count out a good quality bushing reel. They may take longer to break in but once they do thy will run smooth as silk for years of use. Most center pin reels now come offered in a variety of anodized finishes this is a nice feature and enhances the look of your investment, black, gold and silver are the most popular.

When many anglers are looking to purchase a center pin reel they often make the mistake of thinking that this is a reel that they can use for all of their river fishing. While you can use these reels in several different applications you will soon find out that center pin reels are for the most part designed for specialty situations, most common is float fishing in small to medium sized rivers. The main feature that makes a center pin reel so much fun to play fish is also its downfall as far as versatility is concerned. The one to one ratio you get from this reel is okay when you don't have to cast or retrieve a long distance, but if you are casting long distances all day a center pin will wear you out. Also you will not be able to cast as often thus making you less efficient in covering water and you will show less fish your bait. This is the reason that center pin reels are better suited for use on small and medium sized rivers.