Not the hardest thing, but the thing that I spend most time doing during the development of a project is the endless process of zooming in and out within PRV and tweaking velocities and note start times. This applies mainly to piano and electric piano parts.

Razorwit
 
3. Selecting outputs for tracks/sends/whatever. Why? Because output types aren't nested into folders and so I do this when, e.g., adding a send:
 
Dean
 

And this^^

I have trouble working with tempo changes.
 
1. Moving song parts around when changes are present.
2. Setting tempo when capturing an idea and/or then fitting to grid.
 
Good threads never really die they just return like the living dead...  

I'm not sure you really want Sonar to make drum tracks for you automatically.  Drummers have very specific things to do in most songs that have to do with understanding the phrasing, chord progression, melody and various important parts of a song or composition.  Sonar is not really designed to make great use of these things as automation.
 
With that in mind, there are a few techniques towards creating a good start...
1.  Make sure your meter is set correctly.
2.  Make a few "sample" bar patterns that work well together and convert them to groove loops.
3.  Stick with one drum synth and sound (kit) to begin with until you have a solid line.
4.  Do your best to keep the drum lines mathematically metrical until you have really solid parts.
5.  Use the MIDI filter to copy individual drum parts to other parts, i.e. move the high hat to the ride.
... once you have good loops, it is a good idea to replace them with copied (non-loop) parts so you
can modify individual hits, fills, flams and crashes.  Be careful about your cursor placement and quantize
settings as they can modify great lines into aweful parts (this isn't a Sonar problem; all sequencer programs
do this).
 
Personally, I use a lot of techniques to get great drum lines in Sonar, Pro Tools, Nuendo and Finale.  Some
are very time consuming.  Depending upon the style, I usually imagine I am performing the drum parts and
imagine the physical things I would do on an actual percussion instrument kit(s).
 
I hope this is helpful,
 
Tom
 

As per your original post about "What's the hardest thing you do in Sonar?", I find working with the staff view very difficult.  I've read many posts and comments that agree and that Sonar isn't really interested in doing too much to it.  I have my work arounds (mostly by going back-and-forth with Finale) and some suggestions I've read in the posts about 'silent' notes to access various ledger line notes. 
 
I kind of wonder why Sonar hasn't made an agreement for licensing with Finale like Pro Tools did with Sibelius (yes, I am aware that AVID did eventually purchase the company).  Finale actually lacks a lot of cool Sonar processing so it would be a win-win...
 
... of course, I expect a great deal of comments pontificating about why working with real musical notation is old school, stupid or just fine in Sonar.  I hope these commenters will understand that I am answering the posted question.  I won't be arguing how others feel about actually writing/reading traditional music scores, parts or nomenclature.  Your process of creating music is your own and my process is mine.

What's the hardest thing you do in sonar?

 
The hardest thing for me is turning it off :)

Razorwit
3. Selecting outputs for tracks/sends/whatever. Why? Because output types aren't nested into folders and so I do this when, e.g., adding a send:
 

 
Just my .02.
Dean
 

+1
Selecting proper item from this list is an achievement when I use two Fireface 800 units at once: there are 56 inputs. Left / Right / Stereo increases count even more.
 
Nested folders would be a great improvement.
 

For me it is the slice and dice drum editing (multi-track acoustic drums). Audiosnap is not very intuitive, and even when you do figure it out - the results are often buggy/glitchy sounding. Even sometimes when there are only a few samples/milliseconds of correction.

Not being able to freeze multiple tracks is my biggest problem. (don't want to use duckbar) 

Midiboy

vanceen
Moving around take lanes, especially moving take lanes from one track to another. They proliferate so fast that you run out of vertical screen space quickly and have to move groups of takes in jumps, i.e. drag, sroll, drag, scroll...

I'm trying to understand.  Why would you move take lanes?  That defeats their very purpose.  Leave the take lanes and use comping to create the final track. 

That is a narrow view of their "very purpose". There are myriad cases where I (and folks posting in other threads here) ) want to easily be able to move / copy clips from one take lane to another, but find it a PITA. Can really slow down types of editing / comping.