I ran into this difference:

---
irb(main):001:0> VERSION
"1.6.7"
irb(main):002:0> "nan".to_f
NaN
---
irb(main):001:0> VERSION
=> "1.8.2"
irb(main):002:0> "nan".to_f
=> 0.0
---

(1.8.2 is really 1.8.1+1.8.2pre2-1woody1 in Debian)

I wouldn't have been surprised if it was the other way round. Can
anyone explain why it is so? Seemed like a nice feature to me.

-- 
Thomas
beast / system-tnt.dk