No substitute for the real thing??

I pose this question as it relates to granulated sugar versus Splenda. I was approoached to do a birthday cake for someone using splenda. I'm always up for trying new things, especially when it may potentially result in a delicious new discovery. I'm even more excited when it may broaden my customer base. With so many people counting carbs, watching their weight or more importantly adhering to a special diet because of a medical condition, a baker/chef stands a good chance of having atleast the occassional customer inquire about goods made with reduced sugar or sugar substitutes right? Well anyway, on with my story. I've heard so many times, "Oh Splenda tastes just like sugar - in fact it is sugar!!" Me being the eternal skeptic found that sooo hard to believe, so I tried it..and to those people I say "get outta here!!" It's much much better than those artifical sweeteners, and much healthier I would imagine. But I tried some in my coffee some months back, and according to the package 1 tablespoon Splenda = 1 tablespoon sugar, so then my normal 2 teaspoons of sugar, should equate to 2 teaspoons of splenda for my coffee correct? Well it didn't!! And I noticed some peculiar little fizzy bubbles rising to the top when I spooned that stuff into my mug of coffee. Umm is that normal?? Well, I didn't die after drinking it so I guess I'm safe. Yeah, yeah I'm rambling right?? Sorry..geez So anyway, I agreed to do the cake of course, but made a point to reiterate that this was a total experiment for me!! I made sure to let them know that if I could not find a recipe on the Splenda website I was going to have to adapt one of my own and "hope it turns out". I immediately got online & diligently scoured the Splenda site, found a recipe for yellow cake & made sure to read all the helpful hints & tips. I baked the cake Friday afternoon, after 2 trips to the grocery store - 1 to buy buttermilk & Splenda for the cake. The second trip to exchange the Splenda for Splenda Baking Sugar Blend. Yes boys & girls, there are multiple types of Splenda. That little yellow box requires various alterations to your recipes and can not be used in baking something that needs to rise, such as a cake. So I exchanged the itty bitty $4 box of Splenda for the 2lb $7 bag of Splenda Baking Blend. Both quite pricey if u ask me. Anyway, the cake was a sucess from what I've heard thus far. The batter was quite a bit thicker than my "regular" cake batters normally are, and cakes don't rise quite as much with the sugar substitute, so I knew to expect that & didn't freak out at the flatness of my cake thank goodness..lol And I finished the cake off nicely but a buttercreme frosting. Unfortunately, on such short notice I wasn't able to come up with a GOOD recipe for frosting using any type of Splenda..that will be on my to do list..lol I can't seem to the get photos posted at the moment..I dunno what the problem is. Any suggestions?? I didn't think my html knowledge or my copy & paste skills were that bad..lol