I don't think waiting for Leopard qualifies for the same answer always given.
"There is always something better around the corner."
Yes there is blu-ray, new intel cpus, better gpu, 802.11n blah blah blah. Those things are forever changing. You can't stay ahead of the curve.
With an OS, you have a little more time. We have had Tiger for awhile now. With Leopord so close, it makes sense to wait. Especially considering I think Apple will drop some surprises on us for MWSF. An earlier shipping date to lay it down on Vista is very likely.
Of course if you NEED a computer RIGHT NOW. Then yes, you have no chance. But if you have the ability to ask if you should wait, my guess is that you can and you may as well.
Waiting for hardware is silly. Waiting for the OS is a smart move as it saves you money on the upgrade. Wait for MWSF at the very least for more Leopard information.