Any comments on upsampling?

I have an extensive collection of redbook cds and am in the process of purchasing a new unit. Any comments regarding the pros and cons of upsampling from those of you with direct experience? Thanks for your thoughts!
I would worry more about the design and sound of the piece than the technology. There are no absolutes. Everything depends on how the technology is implemented. Either design has the potential to sound great or like crap. I just compared a well regarded non-os DAC to my upsampling DAC and preferred the upsampling unit, but I honestly think the design and additonal $400 worth of parts is what made me prefer one over the other, not necessarily the upsampling
I agree with Phild. ARC prototyped the CD3 with and without upsampling. They prefered the one without, and that is the one they sell. So let your ears be the guide.
I ordered and received a MSB Link DAC III on Thursday and installed it in my system. I used a decent coax digital cable (Tributaries Silver)to go from the digital out on my Rotel RCD 1070 to the dac. This dac upsamples to 24/96. I adjusted the analog filters at first to allow less filtering but I ended up putting the filters back where they were. It sounded a little too mechanical in less filtered stage but sounds incredible now. I'm really pleased. By the way, I listened to an Arcam DiVA CD 73T today that upsamples and it sounded pretty good also. I think my combinations has a much wider and detailed soundstage though.

I'm no digital expert but I have listened to a few dacs recently that seem to finally, properly be executing digital circuitry to the full potential of 16 bit/44.1k. Compared to a few upsamplers I know of these two 16 biters (listed below) are embarrasingly superior. Completely non-digital yet extracting what sounds/FEELS like everything on the disc. Just a handful of times have I completely forgot about the medium and liquified into a perfectly reconstructed musical moment in time. I only had a short time with the Progression dac but was convinced so thoroughly that I had not heard the potential of 16/44.1 that I purchased the new Highly rated AVA 16/44.1 "DONE RIGHT" Omegastar dac @ $1k. I've had it for a month and a friend brought over his BelCanto dac2 and the AVA was clearly much better. The bass is MUCH better. Deeper, stronger, much more resolved and articulate. I've owned the top "platinum" MSB upsampler dac that really falls way short, along with many others, to what 16/44.1 done right is capable of. These links are very interesting. Good luck and happy listening.
just wanted to add...Like you I have an extensive CD collection. A few years back my considerations were taking me toward SACD's yada,yada,yada. But after listening to many universal players (I wasn't about to discard my CD's) I realized to get a really great (NON-DIGITAL) sounding U player would cost me several thousand$. What I am listening to now cost far less with better performance. My digital front-end is a Sony DVP-7700 (transport), soon to be modded/optimized, connected to a OmegaStar dac with a $100.00 Harmonic Tech digital cable. This set-up produces world-class transparency, is absolutely non-fatiguing and is about as good at resolution as i've ever heard. Dynamics, rythym, shimmer that most 24/196 boxes hope for.

Omegastar dac $999.00
Sony DVP-7700 $234.00 delivered E-bay
Harmonic Tech Dig. $100.00

You don't need to spend big money any more to get HUGE performance. At less than $1500.00 I have world class digital playback. I'm a very happy camper. Enjoy them bits.