Software is definitely lagging behind the hardware. I have very few programs that take advantage of my four core hyper-threaded machine. As these processors become more commonplace you would think optimizing software for them would be a great selling point.
You'd think so! I have a P4 Hyperthreading processor and it is rarely pushed to the limit! One core two threads and linux actually does a pretty good job of using it! One of these years I'm going to bump my head on the low ceiling and have to get new hardware, but it hasn't happened yet! My machine actually works better now than it did last month! Ubuntu 10.04 is really nice, and actually faster on the same machine!
It really depends on the problem the software is trying to solve, most problems don't actually benefit enough from making a parallel algorithm to solve it.
The future is in virtualisation, you can have multiple operating systems (typically windows, linux, solaris) running concurrently on a single machine .
For a single OS running applications its overkill (unless your a gamer) but for industry there are many reasons why you would need instant access to different Operating systems from your own machine and multicore processors are essential for best performance.
I was thinking of gaming and video encoding.
My friend has an AMD 6 core - available for consumption now and rather inexpensive. The benefits are noticed when encoding and multitasking.
There is a FRY's special now with a 6 core motherboard for ~ $210.
Apparently I need a new computer. 
I just got some bad tech news too, Zemmy. The computer I have been upgrading since 1992 (I am not kidding here) has been maxed out. To replace yet another motherboard so that I could upgrade to yet another chip would cost more than just buying a whole new desktop.
I am finally going to have to buy a whole new computer some day soon. 
The computer I have been upgrading since 1992...
Photo:
Gramps performs his latest computer upgrade.
ENIAC contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and around 5 million hand-soldered joints. It weighed 30 short tons (27 t), was roughly 8.5 by 3 by 80 feet (2.6 m 0.9 m 26 m), took up 680 square feet (63 m2), and consumed 150 kW of power.
thems some sawheeet hardwares
Here's one heck of a deal Gramps:
http://www.walmart.com/ip/HP-1-TB-HP-P6310F/13377123?sourceid=30959685013032165248
lamparty
This also holds for Non-Mac machines also! The main advantage of Multi-Core processors is in Multi-tasking! I don't often actually have active 4 programs that are actually all working at the same time, Open yes, actively working, no! Most computer tasks I do are finished by the time I can switch from one program to the other, except for something downloading in the background! I can see though were people that convert and manipulate large video files and use Photoshop or GIMP to alter photos might be able to do something else while the process finishes! But how many of those heavy task does any normal user ever have running at once? So Dual-core Tri-Core and Maybe Quad Core I can see, but beyond that is going to take a whole lot of software optimization before those extra cores are usefully for much of anything!