Limit to number of rules?

I have been plodding through creating rules for all the newsletters, etc that I am signed up to and have already created a 100! I have just taken a look at what remains in my Inbox sorted by sender and reckon that I still have another 200-300 to go (arrrgh). Are there any known limits - physical, logical or performance wise to the number of rules that one can have.
And just to repeat again - I do think it would be helpful if one could simply specify the default topic for each contact. If I had this facility, then I think this would cover about 95% of the rules that I have currently set up.
And just to repeat again - I do think it would be helpful if one could simply specify the default topic for each contact. If I had this facility, then I think this would cover about 95% of the rules that I have currently set up.