Just to point out that the PM 1.6ghz has an 800mhz FSB vs the iMacs 533mhz, a slight difference. Also, most people's complaitns about the iMac focus around the crappy, non upgradable GPU, and with this system, you may have a crappy GPU but at least you can replace it.
Also, as for the comments about the benchmarks of all the Macs, I just don't trust XBench to be accurate at all when comparing machines with different processors. Yes, it's an accurate way to compare machines of similar architecture, but for comparing a G5 to a G$ system, for example, I don't think it's very effective.
Example, in Xbench tests, the CPU score for the 1.42ghz mini is as good or better than an iMac G5. However if you look at some realworld tests, like Cinebench or MPEG4 video conversion, the G5 stomps on the SP G4 systems. It really is pretty clear, imo, that XBench is pretty inaccurate when it comes to G5 vs G4 comparisons.
I will freely admit that some (all?) of the G5s have a issues with disk IO operations. Maybe this is a problem with the IO controller, or maybe it's a software issue and future upgrades will improve it. Hard to say as I am not an Apple engineer.
All that said, for all around performace/price, you can't beat the mini...
Rob