Hey there…
I am working on a model and for a specific part of it I need to exturde a cone out of a cylinder…I did manage to do it and keep it all-quads, but I get a bit of a messy topology, and also I get unwanted corner sharpening of the cyilinder…
Does anyone know how I might deal with an issue like this?
Here are the pics :
You could use boolean-modifier, or array-modifier.
another way would be to knife project a circle with more segments and extrude it !
happy bl
Another alternative solution is to use a shrinkwrap trick
Make a duplicate of your cylinder, from before adding the 2 loop cuts you’ll need for your cone
Move it to another layer
On the original object, you make your loop cuts and the cone
Select all the vertices of it, minus the actual cone, then assign them to a new vertex group you create
You add a subsurf modifier to the duplicate cylinder from the other layer, set it to the level you want/need
Then on your original cylinder+cone you add the samesubsurf modifier, same level
Then you add a shrinkwrap modifier that target the duplicate cylinder and only affect the vertex group you created and assigned vertices to
Thank you all for the useful replies 
I did try Sanctuary’s solution… unfortunately I get some nasty results just around the cone extrusion… any idea why it might be happening?
The new intersect tool in Blender 2.72 will be your friend in solving this particular problem. 
Other than that, it’s a matter of maintaining consistent edge spacing to maintain the circular geometry in subdiv/smoothing. If it isn’t you’ll get pinching. Loop tools plugin has something for that.
