I really needed something to get my thoughts down and in this day and age using a cassette deck just seemed way too limited from the get go. After doing much research on digital recording (both DAW & PC software) the Korg D16 just seemed to have the right features for the right price (I bought mine used from eBay at about half the current new price). For the price you can get one used, I just don't think you could hope to find a better solution to your recording needs. The D16 is a LAPTOP STUDIO--literally--I set mine on my lap while I am playing keyboards, and everything I need is right within easy reach.
Yes, it does have limitations, such as limited harddrive space (especially if you have the older version with the 2.1 GB drive instead of the 6 GB drive), but most of these limitations can be worked around. I immediately purchased a Jaz drive to use with the D16 because you can use it just like a harddrive. Record you song(s) track(s) and dump them to a Jaz, CD-RW, or external SCSI harddrive, and then clear out the internal drive for the next song to record. Even with the 2.1 GB harddrive, you should be able to use the D16 to record a full session without needing the external devices. If you have a CD-RW, you can also master your own CDs!
The touch panel makes this the most intuitive recorder on the market--period. I tried most of the big names, including some of the $3000+ models and none were even close to the D16 in user friendliness. And most didn't offer significantly better, or more, functions than the D16 did.
On the down side the inputs can be noisy and the internal harddrive is certainly always noisy, but liveable for most applications. The biggest downer is that the S/PDIF connections can't be used for ADAT which is a shame since Korg was so close on that one. This will limit it's ability to grow with you if you need to add more multi-tracking capability as your requirements grow.
Software upgrades are a breeze if you follow Korg's instructions specifically (go to www.korg.com and type "d16" in the search box). Don't even bother with the rest of Korg's website because it is no help. There are no user groups or any other kind of help other than the software and manual downloads.
Never mind the limitations, if you need a notebook for your music ideas the Korg is the perfect choice for a very modest price. Plus, you can also use it and it's effects to make a decent master CD: one at least as good as most small commercial studios would produce (i.e. demos and promo recordings).
Conclusion: very nice for the price!