Is there a way to make them stiffer? Not adding so much butter?? More sugar syrup? Cooking the sugar a little warmer?? I have NO clue about any of it as you can tell. I love IMBC.. but it's so soft. I wanted to make some of Cambo's cupcake bouquets and I was thinking that the IMBC might just slide off. It's getting a bit warm here (in NH) and I don't want it to be a flop. Are there any other icings that are sort of like an meringue based buttercream that are more firm? I love the smooth texture of the meringue buttercreams.. so good.. I guess I am just fishing for ideas here.. LOL. Thanks for any help..
If you put the IMBC in the fridge it will get a stiffer. But don't leave it in there for too long or it will become hard......like the butter it was made from.
I don't think IMBC will hold up very well if left out in the heat. Maybe you would be better off looking for a whipped buttercream recipe. There are some here on this site that are pretty good. Take a look in the recipe room.
I should say that the heat is only about 80 degrees and it's less indoors (we are just coming out of the cooler weather so anything feels REALLY hot to me right now.. LOL) And also.. I hate the grainy-ness of american buttercreams, but I will use one if I have to.
I have had some experience with that. I regularly make IMBC and I have to admit it can be quite hit and miss how stiff it is. I recently made a batch which turned way too soft. I realised that my butter was a bit on the soft side to start with, so put it in the fridge overnight in frustration. I took it out next day, let it come to room temperature and re-whipped it. It was better than the night before but not great. That got me thinking that maybe the ratio between sugar, eggwhite and fat was off. The next time I decided to weigh my eggwhites. My recipe calls for 5 eggwhites, or 150 grams. Turns out 4 of my eggwhites were already 160 grams, so I had been adding too much eggwhite all along. I proceeded with the correct weight, and the result was perfect. The IMBC was perfectly stiff and easy to work with.
I use this recipe:
http://www.baking911.com/asksarahbb/index.php?showtopic=913
I personally like to use European style butter in my IMBC. It has more butter fat in it. 
I have cut the amount of butter in my recipe down from 1 lb. to 12 oz. or 3 sticks. IMBC or SMBC are both softer than powdered sugar based icings, but it is not runny if it is cooked to the correct temperature and the butter still has a slight chill to it when you add it. Also it has to be beaten long enough, you will notice a difference in the sound of the mixer and the beater when it is done. It makes kind of a slapping noise as it mixes.
http://www.cakecentral.com/cake_recipe-2426-Italian-Meringue-Buttercream--Shirleys-Method.html
I have made your IMBC Shirley and love it.. I am just wondering about the heat.. I'll have to experiment with it in the heat. Thanks for all of the advice.. keep it coming if you can think of anything else. 
Jeanne I will be honest with you, IMBC does not hold up in weather in the 90s and above. I did a wedding cake last July with it and the temperature that day was 117 degrees! Thought I would faint at that wedding, and I did have to take the tiers apart before cutting as they were beginning to slide, even with doweling. Tarzan couldn't have stood up under that kind of heat!
Oh Shirley you are brave.. it's supposed to be in the upper 60's this weekend so I don't think it'll have too much of an issue with it. It's 86 today though and PHEW.. I couldn't do 117 degrees.. especially if there was any humidity involved. I just want to make these cupcakes for mother's day and I want them to have the best frosting.. IMHO it's IMBC.. so another question.. I have heard that it is tricky to color??? Is that true?
I use Americolor gel colours for my IMBC. Yes, I have had problems with the darker colours. I sometimes find that the colour will separate out and pool at the bottom of the bowl. I posted a question about that here on the boards and someone suggested that I should let my icing rest after mixing the colour, and that really helps. I also tried to experiment with Flo-Coat, which is a product from Americolor which turns their gel colours oilbased, which is useful for tinting chocolates. Anyway, adding Flo-Coat made my IMBC too soft, and side by side with the "rested" BC the colours were the same.
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