The Mac Mini will run InDesign, Illustrator, Bridge and Acrobat reasonably quickly with the processor/RAM setup that you have selected. However you should be aware that as with any "cheap" machine there are downsides.
The graphics processor, whilst adequate for general use, will struggle a bit with bigger files and complex routines in Photoshop because it shares the main memory with the CPU. The standard HD is 320Gb and you may find this fills up rather quickly. With a small memory foot print, its essential to keep a reasonably large amount of free space on the HD to avoid Photoshop slowing to a crawl as it struggles to find space for its image file when you work on larger files.
I know you have ruled out a Mac Pro on the basis of cost, but if you can find the extra cash, a 27 inch iMac is a much better proposition with its separate graphics card, superb display and much larger HD than putting any more money into a Mini to buy the faster processor. The iMac also offers you the opportunity to add more RAM which the Mini does not. More RAM will always give cost/performance benefits, and I would always recommend extra RAM against a more expensive faster processor, though both would be good if the cash is available!
Quite a few of my clients run CS4 on recent 27 inch iMacs in a day-to-day studio situation and find them very good. Some have upgraded to CS5 and have commented that they see a slight increase in performance over CS4.
Thanks for your comments.
My concern with the iMac's is the quality of the colour on the display. I know someone who has one, and even after using a hardware/software colour calibration tool on it the colours are not as accurate as on a separate Apple Cinema Display (which I already own). In fact on one file a background which is supposed to be red looked pink!
If you already own a Cinema Display, check that it is supported by the Mini. If the Cinema Display is fairly recent there should not be a problem.
Regarding the iMac displays, I suspect that there may be something wrong with the calibration on the one whose owner you know as my clients who are using iMacs don't have a problem with colour.
That colour accuracy was with the old Aluminum 20" iMacs. Those displays were 6 bit, using software dithering to get millions of colours (vs. true 16.7 million colours on 8 bit screens). The new 21.5" and 27" iMac use 8-bit monitors with LED backlighting. The one problem you might not like are the glossy glass, since it increases the contrast vs. Matte that is more accurate to printed colours (CMYK).
Also there is a new Mac Mini out that you can increase the RAM yourself (no voiding warranty with Putty Knife).