Difference at 192k compared to what? What bit rate are your songs at now? 128? 96? Either way, yes there will be a difference. At 128k there is highly noticeable clipping and compression noise, and music at 96k is virtually unlistenable! I notice a difference between 320k and 192k when playing back at home, cos I have a half decent amp and fairly good speakers. I also notice the difference between 192 from the computer to amp (optical connection) and the same song : 192k from my ipod to amp (cheap analogue cable). However, my amp isn't super dooper high fidelity, so I notice very little difference in 320k rips from PC to amp, than the original CD from my DVD player to amp. One of the few I do notice it on however, is Rage Against The Machine's self titled debut. Play that back @ 320k from PC it sounds fine. Play the CD down a good pair of analogue RCA's from the DVD player and it sounds superb. But then, it is one of the best recorded albums ever!

As for how many your ipod will hold, I couldn't tell you. But my 60 is is filled at about 9k songs @ 192k (some are 128, can't be helped sometimes), so halve the capacity, halve the amount. So 30gb would be 4,500, add a few for the extra 2gb, maybe 5000-5500? Depends entirely on the lenght of the song to be honest. 100 songs at 30 seconds each won't take up anywhere near the room 1000 songs at 10mins each will...