I love so much yahoo pipes that I would gladly pay for it (an amount like or above a yahoo plus for email -$20- is ok) ! This should assure us that Yahoo pipes won't disappear in the future (like saying goodbye to the free yahoo alerts).
IMHO there are no other serious competitors to this product. Furthermore, I have spent a huge amount of time creating my hundred of pipes. I am hooked ! ;)
The only thing that is missing for me is a way to get emails with rss pipes : I would like to tell the machine: check this pipe every day or every hours or only such days (Monday through Friday...) and send me an email with the (only new) result(s).
Currently I am using the software websitewatcher (its features for rss feeds : sending new results only and updated results). The problem is that I need to let my computer awoke 24/24 7/7 and that it can't keep more than 100 results per email ! ;(