I have been coding in C both as a hobby and professionally for about 16 years now, but always for userland code (i.e., programs, not kernel or drivers). Most of my jobs involved high level languages (I have done a lot of Perl and Ruby programming, with the occasional Java, Python and shell scripting in between). I did develop a lot for MS-DOS (which was probably as close to bare-metal programming as you would get on a x86 machine), but my last job involved 5 years of Perl and Ruby on Rails web development.
That being said, I am now a senior engineer for embedded Linux development, developing drivers (including an emulator for a legacy simple microprocessor inside a kernel module) for uClinux on the Blackfin platform. There are times when my inexperience with hardware related issues (i.e., floating signal levels due to lack of a pull-up/pull-down on a pin) did get in the way, but it has been mostly a highly enjoyable and thrilling experience. As stated by others, understanding your tools is essential -- for uClinux, that meant the GNU Toolchain, which fortunately I was already familiar with due to my background on FOSS technologies.
The Blackfin is hardly an entry-level microprocessor (in particular, it does not have a MMU, which has some relevant effects on Linux development), but as already stated, you can buy a Beagleboard for around US$200 with all required accessories and start messing around with it in just a few days. If you want something simpler, there are many Arduino options out there, though if you have some real development experience under your belt I believe you will find their development environment a little limiting (I know I did).
After you get comfortable with your tools you might want to spend some money on an in-circuit emulator (or ICE). These are usually highly platform specific (both in terms of target architecture and development environment), but are highly recommended for anything beyond the usual blink-LEDs-after-button-press examples I am sure you will quickly outgrow.
In few months you will find yourself building custom images for hackable customer devices using Buildroot and having a lot of fun. All I can say is, go for it, it's highly addictive and not particularly expensive to do nowadays.