PERF: Too long MultiIndex repr freezes notebook
I have a quite large MultiIndex here that I accidentally tried to show with `__repr__`:

``` python
print len(counts.index)
print type(counts.index)

3982319
<class 'pandas.core.index.MultiIndex'>
```

whereupon my Macbook started to boil and the notebooks became unresponsive and I had to hard-kill the notebook server to get things back on track.
Is that avoidable somehow in a similar fashion you are checking the length of a dataframe before showing it?

Pandas version is 0.13.0rc1, with Canopy's python 2.7.3
