The new mac mini is provided without superdrive (external USB model priced 79 $), a thunderbolt port, a Core i5 processor (2,3 Ghz or 2,5 Ghz) or Core i7 2,7 Ghz (as an option, 100$ only), dual core however with TurboBoost and HyperThreading, an Intel HD3000 chipset or a Radeon HD 6630M (256 Mb of dedicated GDDR5), and 2 or 4 Gb of DDR3 at 1333 Mhz. A 256Gb SSD option is available for 600$.
The server model (priced 999$) brings a quad Core i7 at 2Ghz, and the 256Gb SSD only option is available for 400$ more (550$ with both the SSD and a 750 Gb 7200 rpm hard disk). However it only features the Intel HD 3000 chipset.
The base memory is 4Gb (2Gb on the entry level model), however we still have to replace both modules to reach 8Gb (required to achieve max performance and for audio applications).
The Core i5 processor at 2,5 Ghz is up to twice as fast as previous Core2 Duo 2,4 Ghz one (also thanks to the faster memory bus), and the server model is up to three times faster. The Radeon HD 6630M dedicated graphics card is also up to two times faster than the Nvidia 320M chipset (see here and there).