I always clean my fretboards with only warm water.
When you clean it on every string change, they dont get very dirty so you don't really need any products to get it clean.
WIth water, you cant really go wrong, but you should oil your fretbord slightly after each cleaning aswell.
I don't use lemonoil, however. I use a oil substitute, can't recall the brand but it's a red liquid in a spraybottle, it does the job perfectlly.
If you want more info on the product, I can come back with more info when I'm in the same room as the bottle!