No details yet, so keep watching to see if the Mac Pro looks crippled and/or overpriced next to the Dell, or whether it turns out to be a good value.
update:
Guess we go with crippled
*and* overpriced.
My guess would be that the T3500 is the Xeon 3500 in Dell's mid-tower case, with 6 RAM slots. T5500 would be a pair of Xeon 5500s in the mid-tower, and the T7500 a pair of Xeon 5500s in Dell's maxi-tower. Interesting memory limits, though, for the dual socket systems....
T3500 - six RAM slots, one socket (air baffle on/off)
A current T5400 (up to 32GB RAM, 8-core) equipped as such, as similar to an Octo 2.26Ghz:
PROCESSOR Quad Core Intel® Xeon® Processor E5440 (2.83GHz,2X6M L2,1333) edit
OPERATING SYSTEM Genuine Windows Vista® Business Bonus-Windows XP Professional downgrade edit
2ND PROCESSOR Quad Core Intel® Xeon® Processor E5440 (2.83GHz,2X6M L2,1333) edit
WARRANTY & SERVICE 3 Year Limited Hardware Warranty with Next Business Day On-Site Service edit
VIDEO CARD 256MB PCIe x16 nVidia Quadro FX570, Dual Monitor DVI Capable edit
CHASSIS CONFIGURATION AND 1394 Mini-Tower Chassis Configuration edit
MEMORY 4GB, DDR2 SDRAM FBD Memory, 667MHz, ECC (4 DIMMS) edit
OPTICAL DRIVE 16X DVD+/-RW w/ Cyberlink PowerDVD™ and Roxio Creator™ Dell Ed edit
RAID CONFIGURATION C1 All SATA drives, Non-RAID, 1 drive total configuration edit
HARD DRIVE 750GB SATA 3.0Gb/s,7200 RPM Hard Drive with 16MB DataBurst Cache™ edit
MONITOR Dell 19 inch™ E1909W Widescreen Flat Panel edit
SYSTEM DOCUMENTATION Resource DVD - Contains Diagnostics and Drivers
Sorry about the garbled text, it's a cut and paste.
$4133.
The supposed "starting at" prices are BS for Dell, Lenovo, and HP. By the time you get to something comparable, it's not that great of a deal.
I'm not saying Apple still isn't overpriced in some areas, but the others aren't cheap either.
Also, Apple really doesn't offer anything equivalent to the 7500 or 3500. The quad is still quite a bit high for Apple. It's basically an HP XW4600 for a grand more (XW4600 is a quad, single socket, 8GB max RAM, ~$1500).
In my opinion, the quad MP really should be about $1800-$2000, to bring it in line with HP but with the infamous "Apple tax".
EDIT A current T3400 comes in at about $1600-$1700 (2.66Ghz quad, 2GB RAM, 750GB HD) so it would make sense for Apple's 2.66Ghz quad to run $2000 or so.
Also, something that really does irritate me with the new MP, though it's not a deal breaker, is the fact that no Quadros are being offered. I could have sworn the last gen was available with a FX5600, which is a nice card.