Why does grep hang when run against the / directory?

My question is in two parts :

1) Why does grep hang when I grep all files under "/" ?

for example :

grep -r 'h' ./

(note : right before the hang/crash, I note that I see some "no such device or address" messages , regarding sockets....

Of course, I know that grep shouldn't run against a socket, but I would think that since sockets are just files in Unix, it should return a negative result, rather than crashing.

2) Now, my follow up question : In any case -- how can I grep the whole filesystem? Are there certain *NIX directories which we should leave out when doing this ? In particular, I'm looking for all recently written log files.