I just switched to a less poweful conmputer (AMD Phenom II X3 710, $HOME on NFS, 2 screen) and I can see a slowdown. This may exist on my other computer, but given its horespower it is not noticeable.

I have 75 tasks in my Inbox and it takes a lot of time at 100% CPU whenever I switch to the Inbox.

I use Chrome 33 on Linux.

I have profiled the application using the Chrome tool, and get the following data:
Self | Total | Function
52.67% 52.67% (idle)
11.45% 11.85% Date.setISO8601
7.93% 8.23% Time.strToDatetime
4.17% 5.88% b.toString
3.96% 10.50% (anonymous function)
2.30% 2.30% (program)
1.79% 1.79% RegExp: ([0-9]{4})(-([0-9]{2})(-([0-9]{2})(T([0-9]{2}):([0-9]{2})(:([0-9]{2})(.([0-9]+))?)?(Z|(([-+])([0-9]{2}):([0-9]{2})))?)?)?)?
1.38% 1.38% (garbage collector)
1.19% 36.45% a.startAt
1.03% 16.36% Time.nDateToBegin
0.84% 40.58% (anonymous function)
0.82% 0.82% nc
0.69% 0.78% Time.timezoneToFullOffset
0.61% 8.83% Time.userDay
0.61% 10.92% Date.format
0.54% 9.08% Time.setDateTime
0.54% 43.06% i.$digest
0.43% 4.84% Time.strToDateObject
0.37% 0.37% (anonymous function)
0.35% 9.00% Time.setTodayDateToLocalDate
0.34% 1.11% Time.getUserOffset

I am a bit surprised by the time spend in date related functions and by the CPU usage, it makes the whole application extremly slow.