A lot of people holding on to dinosaurs... 2006 was 8 years ago, yet I still see Core 2 machines everywhere. Pentium 4 era machines are very rare, though. I see the occasional Athlon 64... probably the oldest line I see on a somewhat regular occurrence. Everything else has croaked, or is too slow to use.
Come to my university, Core i is practically non-existent, core 2 is pretty rare and the majority are Athlon 64s and Pentium 4s.
Computers in my lab include an old core 2 duo system, an ancient p4 computer and an even more ancient and slow celeron desktop from the p4 era (single core) -- not fun for matlab and statistical computations. Newer machines include a i3 (came with equipment so doesn't count as its not being used for general usage) and an i7 (currently not in use because you know, logic). A P3 with win 98 drives most of the equipment.
The library computers are better, lots of core 2 system with the occasional pentium, i3, i5 or i7 some p4s (it just seems that they throw systems out there, you will see i7s, p4s and core 2s side by side in the same chassis). However around campus core 2 and p4 rule the roost. Win xp everywhere.
I am honestly surprised at how snappy those old systems are. Running a bare xp install, browsing performance is very good and heavy excel usage isn't a problem.