I got a PN-20 to play with, and while I'm not yet ready for it to replace my 60CS for Geocaching in a firmware revision or two I might be. There's a lot of information available on DeLorme's forums, but here are my quick impressions.
The topo maps and aerial images on the PN-20 are very nice and the aerial images in particular will be helpful for finding caches in unfamiliar territory. That said, once you've used up your 400 sq. km of free downloads they're terribly expensive. You can apparently order them on CD for a lot less than the downloads (I don't understand that pricing model) but even so they're still expensive. You can use their TopoQuad data with the PN-20, which gives you the USGS 7.5 minute quad maps but not the aerial imagery.
Physically, I prefer the 60CS. They're pretty comparable in size, but the 60CS feels smaller and the tapered case fits my hand nicely. The PN-20 is OK, just not as nice. The PN-20 has more battery options. It will take standard alkaline or NiMH AA cells, or you can get a Li-Ion battery for the PN-20 and can charge it in the unit.
The UI is where I think the 60CS really shines. It may just be because I've been using it (and other Garmins) for a long time, but I really do think the 60CS has a better designed UI. Things seem better laid out and more intuitive on the 60CS. Garmin uses bigger fonts and makes better use of graphics, and it's a lot easier on my aging eyes. The PN-20 uses a really small font for most things. Also, the PN-20 feels slow - I'm often waiting for it to do things, where the 60CS is always quick to respond.
I like what you get out of the box with the PN-20. For a decent price you get the unit plus routable streets and good topo data for the entire US (if you live anywhere but the US it's probably not of much interest to you). The additional maps and aerial photos are great, but once you get to like them you'll end up sending DeLorme a lot of money a little at a time.
Anyway, the PN-20 seems very much like a 1.0 release. It's a little rough around the edges now, but I'm pretty confidant that it will get polished nicely. Given that this is their entry into this market, DeLorme has a lot of incentive to get it right. Plus it seems like a lot of the DeLorme engineers are outdoors types that actually use the thing. It has great potential, and I have high hopes for it.