Save your money - your ibook will be fine for the forseeable future unless you're doing absolute cutting edge graphics, video, sound and gaming. It never ceases to amaze me folks who will buy a PB or MBP, nowadays, for using Word, checking email, surfing the Web and watching DVDs.
Yeah, the new MBs are pretty special, but keep in mind they're rev. A machines, there's several new Intel processors waiting in the wings this year, and by the time you actually need a replacement laptop and have saved up for one, they'll really be killer notebooks.
Get your cell phone - it was your original goal. Then start saving again for a MB.
As for me, every product I buy is on a cash and carry basis only, including my Apple hardware. If I don't have the cash saved up, I don't get it - I'm approaching $0 on my credit cards and don't ever want to use them again.
Which leads me to another observation - a lot of Americans finance their lives on debt, so it wouldn't surprise me if a chunk of folks on MR have Apple gear that was purchased on credit cards alone.