Waiting for the "next big thing" never really works. There is always something new on the horizon and you end up never buying anything. I am not a Mac guy so I don't know any release dates for x86 Mactels but unless it is next week, I wouldn't bother waiting. btw, what Mac are you thinking of purchasing? Mini, G5, Powerbook...? That kind of information can let the mac gurus know if you should wait for some really cool upgrade in the near future or not. Of course there are the holiday sales to think about... If I could afford it, I'd buy a mac right now. But PC is always cheaper and more upgradeable. Yeah, I'm a PC fan. But I don't hate Apple.
i bought an ibook about 1/2 months ago, and i love it to be honest i dont think there is any point in waiting because the new Mactels could come out with bugs or faults and all sorts, if you buy one now at least you know it all works fine.
I would also buy an iMac now. The main feeling is that an iBook and Mac mini will be released at MWSF. With the revison of the iMac at the 'one more thing' event, as Samor said the iMac may not be upgraded for a while. Although saying that, its not long to wait until MWSF. If the media centre Mac mini is released, there may be some type of software update for the iMac to support this (though Apple would probably add a tv card to the iMac if this was the case)