Based on the latest Famitsu hardware numbers...
PSP comparisons: After 239 weeks, PSP is where PS2 was at 193.3 weeks (November 11, 2003), where DS was at 102.7 weeks (November 17, 2006), and where GBA was at 161.6 weeks (April 22, 2004).
X360 comparisons: After 187 weeks, X360 is where GCN was at 17.5 weeks (January 10, 2002), where PS3 was at 39.1 weeks (August 5, 2007), and where Wii was at 5.7 weeks (January 5, 2007).
PS3 comparisons: After 139 weeks, PS3 is where PS2 was at 46.8 weeks (January 19, 2001), where PSP was at 69.5 weeks (April 6, 2006), where GCN was at 128.9 weeks (February 29, 2004), and where Wii was at 36.1 weeks (August 5, 2007).
Wii comparisons: After 136 weeks, Wii is where GBA was at 99.4 weeks (February 12, 2003), where DS was at 77.3 weeks (May 23, 2006), where PS2 was at 117.4 weeks (May 29, 2002), and where PSP was at 168.4 weeks (February 27, 2008).
DSi comparisons: After 36 weeks, DSi is where GBASP was at 47.8 weeks (January 9, 2004) and where DSL was at 17.4 weeks (June 28, 2006).
Based on the latest Media Create hardware numbers...
DS vs PSP: Weekly shares of 82.9 / 17.1 are the best DS has done relative to PSP since the PSP un-bump the week before Crisis Core/PSP-2000 hit. This brings total shares to 68.3 / 31.7. If DS stopped selling and PSP continued at this week's rate, it would catch up in 544.4 weeks (December 19, 2019).
X360 vs PS3: Weekly shares of 26.6 / 73.5 bring total shares to 24.8 / 75.2. If PS3 stopped selling and X360 continued at this week's rate, it would catch up in 608.0 weeks (March 7, 2021).
PS3 vs Wii: Weekly shares of 30.8 / 69.2 bring total shares to 28.4 / 71.6. If Wii stopped selling and PS3 continued at this week's rate, it would catch up in 498.3 weeks (January 29, 2019).
Week over week, DS is way up and everything else is down.
PS3 and PSP in particular have some long term downs. To find a lower month for either you'd need go back to October 2008.
Through the first twenty-seven weeks of the year, overall sales are down. However, the systems can be split into camps of 3 up and 3 down. Here's how the year-to-date year-over-year percents stand as of now.
Wii: -62.5%
DSL+DSi:
+7.6%
PS2: -51.0%
PS3:
+5.7%
PSP: -45.7%
X360:
+194.8%
Home hardware: -39.2%
Portable hardware: -22.7%
Sum of all hardware: -29.5%
Last year:
This year:
Looking at these YTD pies, we can see that now both Wii and PSP are down more than a million units from last year.