It definitely is in 8.04. A uname on my desktop shows 2.6.24-19 SMP;
SMP = Symmetrical Multi-Processor. A "live" CD of 8.04.1 shows the same
and my live CD of 7.10 shows 2.6.22-14 SMP.

Probably 99.999% of all apps are written single-threaded and would not
themselves benefit from a multiple-core system. However, if one starts
two apps, each will [effectively] use one core.

If one app has a bug and eats all CPU time, in a dual-core system the
other core is "free" and it's easy to kill the errant process. Multi-
core systems will soon be the norm.