Thread revival! I guess I never answered the original question...
I started out on Mainframes, DEC-10s, DEC-20s, and big iron IBM (summer job during college.) I lusted after various microcomputers, starting with the Altair 8080 and SWTP 6800, with more significant interest in Cosmic Elf 1802 and 8085. Later the PIC came out and was even more interesting, plus AVRs and etc. But it was really difficult to get very motivated to actually do much with them when I had entire ARPANet-connected mainframes to play with...
Eventually the DEC mainframes were dying and I moved (professionally) to high-end microcontrollers like 68000, x86, MIPS, and PPC, where the hardware/micro background was useful for low level infrastructure and driver work. I still seem to enjoy infrastructure development more than actual projects...