Plotting performance deterioration on DataFrames with date-index
The below code-sample gives a big performance drop on plotting in pandas 0.12, compared to pandas 0.11:

In Pandas 0.12 : "Ran in 0:00:29.542475 secs"
In Pandas 0.11 : "Ran in 0:00:06.653506 secs"

It only happens on a date-indexed DataFrame:

from pandas import *
from numpy.random import randn

N = 10000
M = 25

df = DataFrame(randn(N,M), index=date_range('1/1/1975', periods=N))

t0 = datetime.now()
df.plot()
print("Ran in %s secs" % (datetime.now() - t0))
