Over time my SONAR backups are getting larger and larger.  I imaged the C: drive - 'took 2 hours.  Now I'm in the middle of backing up my D: drive (400GB) to an external drive connected via USB.  It's going to take 5 hours...man!  What do you guys do about backups and how long do the typically take? 

Acronis. It's like two or three clicks to kick off the backup routine of everything on my machine (2 TB) to an external hard drive.

I have three external drives that I rotate through on different weeks for the backups. So I have three backups in case anything goes awry.

It takes several hours, but it's hands free and worry free.

I've restored about a dozen times from these backups over the years. Also painless. It's great when something gets installed on your drive and you'd need an IT expert to figure out what's going on. Instead, a restore from Acronis and you're back to where you were before the issue.

I have Acronis.  That's what I used to image the C: drive.  I guess I'm just crying about the time it takes.

I typed this up a long time ago, but still use it. There is no reason to "reimage" ad infinitum, since the vast majority of data is the same. Imaging works great for OS/Programs, but for data files I do incremental backups using xcopy and robocopy. These only copy newer (or non-existent) files, and typically take a few minutes at most (after the first back up pass, which is essentially an "image").

Incremental backup is the way to go. Only the initial backup is lengthy. Then, daily backups are just the changed files. I use Retrospect, works fine. You (OP) didn't mention what you currently use, but the paid-for programs like Retrospect and Acronis have all sorts of features to make backups more efficient, faster, more error-proof, encrypted, etc.
 
Speedwise, it is sort of a non-issue here. My backups are scheduled to run in the wee hours. But if I've done "important" client work or something, I request an immediate backup during a break to go make coffee (or a drink). In my program's (Retrospect) case, it's been monitoring changed files so the incremental backup happens pretty quick, without a humongous drive scan up front.
 
Also, I run encrypted backups every so often, for posting backup files to the cloud. Every so often, the encrypted get put on an external drive and taken to the lock box.
 
In relation to what mettelus has to say about xcopy and such, there is a useful richcopy64.exe utility (I think it is what robocopy became later) that does a poor man's version of incremental.