There's a lot made about whether or not smell is important to a fish, and among those who believe it is, exactly how important.  It was suggested to me at a Bishop fly shop that I try this stuff, so I bought a jar and went about the business of getting it on the fly, and not so much my fingers.

Pros:

• Stays on the fly for a long time even in a swift current.
• Probably hides human smell or the scent of glue and/or gloss used on some flies.

Cons:

• The scent stays on your fingers and clothing for a long time too.
• I personally have never caught a fish with this stuff on my fly.

Summary:

For me, I would rather put the money towards an instructional DVD on improving fly presentation.  In my experience, it's all about presentation and fly selection that catches fish.  Not gimmicks.   I wouldn't judge anyone using the stuff, but it's just not for me.  I want to catch fish on the flies that I tied, cast, drifted, and set in order to catch my fish.  It just feels better to me.

Smelly Jelly might be the hot ticket for other styles of fishing or even people more adept at using bait scent products.  I will not be buying this or any other of the many fish juices on the market, and I would suggest that anyone new to fly-fishing work on their foundational skills before messing with specialty attractants.