I got my new 17" a couple weeks ago a day before an unplanned trip, but left it at home and took my 4 year old familiar G4 15" with me. The 15" may still be a better 'portable' for longer and/or frequent trips I feel at least until I get used to this size deference in my head.
That said, after returning and a few days at home working on the 17" its everything I hoped for in a Macbook Pro. The larger HD screen is amazing, its quick and as mentioned the sound quality is great. Looking at DVDs (my portable theater) is a whole new experience compared to my old Powerbook. For the few hundred dollars more than the 15" this computer will be a huge step up. As for that 'portable' factor, my laptop is used mostly for moving around the house, which I do a few times a day, outside, this room or that, and a weekly trip to our other house, larger yes, but the best compromise for me. I don't really need a smaller size that fits easily in the bag daily and if you think about it and compare its really only a inch bigger each way anyway.
Unless you really need a slightly smaller size its the best option, and in return you get what is a 24" display in a 17" size, bright and detailed gorgeous display also, a slightly faster processor (barefeats tests show it may be clocked a bit faster (10%) than the 15") and better sound - all in all its the maxed Apple laptop (put the 4GBs of RAM in myself, and ordered the 160/7200 HD). This thing ROCKS!