I got the Center 3 today. The sizing is really nice for my setup as it's about the same width as my previous CC-150. It's hella deeper, and somewhat taller, but it's nowhere near as humungous as the CC-390 was and it's not even as big as the CC-290.
Not surprisingly, it sounds way, way better than the CC-150. Very clean-sounding, and it doesn't fade to bleah at the low end like the CC-150 did. It's not quite in the same class as my Studio CC in the other room, but nonetheless I'm quite pleased with the Center 3 given the huge difference in price between the Center 3 and the Studio series.
Before I got this I was wondering why Paradigm didn't release an in-between Center 2. However, it does seem to make sense to me now. In terms of street pricing it is a couple of hundred $ more than the Center 1, but it's also a huge jump in specs, and I suspect a significant jump in quality and range, but without the huge jump in width. In that context, the hypothetical Center 2 becomes somewhat redundant.
The only issue with the Center 3 I've noticed is the slight boominess I can sometimes get with it located in my AV cabinet. As I suggested earlier, I suspect it's due to the rear porting of the Center 3 - not necessarily ideal for a partially enclosed space. I suspect the Studio CC-490 would be better in this regard, but then again it is also rear ported, and it costs almost twice as much. Considering my Center 3 already cost as much as my 42" plasma TV, I figured its pricing was much more appropriate for that system.
P.S. The GF really loves the Center 3, because of its musicality. The CC-150 was simply lacking at the bottom, and the Center 3 fills that range in nicely. It's also quite responsive, without being overly bright. In fact, I think it's crisper than my Monitor 7 speakers. However, my speakers are I believe the first version of that model from 15 years ago or so.