Ok I know this question has been made a hundred times....I've seen the instructions to where you cut out a hole for each tier so it looks crooked but is actually lying even. I tried that once and found it very difficult to center and work with.
However I do not physically understand how some of these cakes can be at such odd angles but still be supported well without sliding off. I know you have the dowels or supports cut at an angle but still...what keeps the tier in place?
I know some of the ones with gentle angles are fine, but the other day on here I saw a beautiful one with the top tier jutting off at almost a 60 degree angle...how?
Mine stick to the fondant under them fine on their own, but if I get nervous I'll dab a little piping gel between the tiers.
If I have a 3 tier topsy or if the top tier has lots of decor that makes it heavy, I hammer 2 dowels all the through the cake down into a base board that consists of 2 foam core boards sandwiching a 2" piece of styrofoam. For heavy cakes, I glue 2 foam core boards together: So there would be a 2" styrofoam sandwiched and glued between a double thickness of foam core boards.
If you use a thick filling, the cakes hold up fine at an angle. But I have been known to bite my nails when a customer asks for a fruit filling in a topsy and try to pesuade them to try a fruit enhanced cheesecake-type filling instead. (It's Bettercreme, cream cheese, cheescake flavored pudding mix, and a fruit pastry filling all blended together).
The ones that are striped with the very sharp angles are usually mud cakes...I don't think i would try that sharp of an angle with regular cake.
What I've been doing is covered the cake with fondant and then cutting the circle out after it firm up. What I really don't like is covering a TT cake that has a hole in it, it just always seem to pull the cake down and make it sag.
I've also heard of people cutting the cake on the top and bottom to angle it so it sits better on the bottom cake....hmmmm, maybe I'll try this for my dd's 3rd birthday cake to test it out.
Thanks!
The angles on that one aren't so bad...I can do that...but I saw one one here (just spent 10 minutes looking for it, can't find it!) where the top tier was jutting off at an impossible angle... was wondering how they did it.
Plus of course I love the ones that are topsy turvy but seperated with flowers or "fluff" but I don't know how to do those either.
Here you go girl!! 
I hope this can help you
http://www.cakecentral.com/cake-decorating-ftopict-611427-.html
I was just about to answer with a link to that exact post! 
You beat me to it!
Here's a couple pics....I think this is what you are looking for. This one was made at the planet cake class using mud cake. http://www.flickr.com/photos/franjmc/2960734442/
Here's a pool of topsy turvy photos on flickr: http://www.flickr.com/groups/topsyturvycakes/pool/
Here's another really nice one that Nati made (also from planet cake):
http://www.flickr.com/photos/natiscakes/2386931085/in/pool-topsyturvycakes
To give the fillings and flatter surface while making the cake appear to have a sharp angle, a wedge is also cut from the bottom of the tier.
Yes!...this is what I was saying in my other post... I'm going to try it this way on my next TT.
Th ebest way to do it is to cut the bottom wedge AFTER you have filled, crumbcoated and chilled the cake. I take it out of the fridge, lay it on it's side (it's fine since the cake is cold - I've never had a problem), remove the bottom cake board and slice out a wedge. Replace the cake board (sometimes I have to trim it again), and voila.
The hard part about doing this is that sometimes I need to prop it up on a styrofoam wedge until I place it on the cake to keep it from toppling over.
Yeah... I know 
I have had one too many disasters with that hole, though, and it is so much easier to skip that step. I don't always carve a wedge from the bottom, just when I think it will give it a better look.
That hole has to be cut so perfectly. Once I thought I carved it just right, but then after the fondant went on it was too small. The next time I thought it was perfect, after spending a couple of hours decorating it the dam began to crack.
Another time I thought all was hunky-dory the dam started sliding off. And my last attempt I cut the hole too big and had to cover the gap with excess decor. Thank goodness these were all trials for my family!
But once I opened Lindy Smith's book and saw that she simply stacks her topsys, I never looked back.
lol..yeah..The trick is to measure the bottom of your cake after is done to know the correct circle size, then cut it a bit(just a bit) bigger than the bottom, cause remeber the sides of the topsy increase in size. I cut my hole after i decorate my cake. I dont put fondant inside the hole. Just buttercream. and you have to be careful when putting the cake in the hole cause if you push on the sides it can cause breakage.
The lindy way is a good way but I would never attempt it in buttercream.
That thing would slide in a second. And most of my clients like buttercream.
Edna 
The top or the sides? For the top, I just use a long serrated knife and start at the top edge, slicing downward. It should look fine once you've rotated the top piece so that the two thick sides are together, like in the tutorial here, creating a more exaggerated wedge shape.
For the sides I stack mine upside down (as per the tutorial) and slice straight down rather than trying to slice sideways - does that make sense? So, if I have a stack of a 6"7"8" tier, I slice from the edge of the 6" down to the edge of the 8", cutting off the ledge created by the 7".
But I center mine rather aligning the edges on one side, like the tutorial suggests.
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