I had a microkorg (the classic one) for a while, but didn't get to much use out of it.
The sounds are pretty nice, but it's nothing you couldn't do with software.
Editing patches is bothersome and unintuitive with the few knobs available, you'd have to get very familiar with all the submenus to feel somewhat comfortable with the editing process, and it still wouldn't be as fast as having a complete layout with all parameters in front of you. It does have a software editor, but then again why not just use software.
I think these little boxes (korg/micron alike) mostly are useful to live performers or people who don't use VSTs (e.g. those who don't like the workflow of software sequencers).
What I have now is a little monophonic analogue synth, the Doepfer Dark Energy. Not nearly as powerful from a sound design perspective as the digital synths comparable in price, but it sounds nice and the most important thing is that there's a knob for each and every parameter. You can really work this thing and get lost in tweaking it.
I can't say that I've used it in a lot of my music yet either (software is still the best for getting things done for me), but it's simply loads of fun.
The fact that it's analogue isn't all that important to me, it's the direct access to everything the synth can do that i find so valuable. I haven't seen any digital synth below $500 that offers just that. Of course, digital synths usually are more complex and thus would require more knobs.
Well, YMMV. There's a pretty high demand for these low budget synths, so I didn't have any trouble selling my microkorg for a decent price. Maybe you have to own one for a while to really know if it's the right thing for you.