Wii comparisons: At 26 weeks (one half year), Wii is where GCN was at 112.4 weeks (November 4, 2003), where DS was at 30.1 weeks (June 26, 2005), where PS2 was at 24.7 weeks (August 18, 2000), and where PSP was at 54.8 weeks (December 23, 2005).
As I've pointed out before, since in this comparison PS2 is hitting a long lull point, Wii has a great chance to catch up. If Wii is flat at 50K indefinitely, it catches up to PS2 in about 2 months. By the end of the year (no holiday bump taken into account), it's ~2 months ahead of PS2.
PS3 comparisons: At 29 weeks, PS3 is where PS2 was at 3.4 weeks (March 21, 2000), where PSP was at 11.5 weeks (February 23, 2005), where GCN was at 15.8 weeks (December 28, 2001), and where Wii was at 4.8 weeks (December 29, 2006).
PS3 vs Wii: Weekly shares 14.1 / 85.9 , very very similar to last week. Total shares now 26.2 / 73.8. If Wii stops selling and PS3 continues at this week's rate, it cathces up in 169.7 weeks (August 26, 2010).
PS2 vs DS: At this week's rates, PS2 and DS meet up in 27.7 weeks (December 6, 2007) at 20.51 million apiece.