I'd say that I break even on my travel reading - lots of offsetting factors:

On the plus side:
- I take a lot of magazine supplements with me that I throw away as I go - these are easy reading and cost nothing extra
- I don't buy newspapers as I get them at the hotel or read them on-line - I'd normally pay for them at home
- I probably surf more when I travel - especially with faster connections at hotels - so don't read as much

On the negative side:
- tend to buy a lot of books and magazines if I am in NYC - Borders Union square and the magazine shop across from the W Union Square do very well out of me - though I'd probably buy these if I wasn't travelling
- I always end up buying books at the airport - just in case I run out of reading

I never seem to get through as much reading a I'd hope when travelling - very envious of those that can get through several books in a two week trip.. but as others may have said - I'd probably end up buying a lot of this stuff (DVDs, magazines, books) even if I wasn't travelling as Ijust like to accumulate this stuff!