I've seen a lot of sites just mentioning the Wireless WII Hack for SNES controllers, but none really reviewing how it worked. I built it and have been playing with it since March this year, so I thought I would give my perspective:

Fabrication:

Early this year, I found the website ppl-pilot.com and saw that it detailed plans for converting an SNES controller to work as a wireless gamecube controller, which could be used on the WII. It consists of two parts: a receiver that plugs into the WII/GC and the modified SNES controller, which contains a transmitter circuit to connect to the receiver. I've worked with electronics before in some circuit classes for computer engineering, so I thought it would be something doable and fun to make. Plus, I really wanted to play some of the virtual console games with a real SNES controller and not the classic controller. It was tough and a pain to do, but it was a great experience.

The first step was ordering the parts. Ppl-pilot.com had a detailed list of components, as well as websites to order them from. Knowing the truth of Murphy's law, I ordered two of each component, bringing the cost to about 110 dollars (including cost of soldering iron and solder). Not the best deal, but better safe than sorry. After a month, I finally got all the parts I ordered and could begin fabrication.

Looking at both the SNES controller and the receiver instructions, I started with the receiver, since the creator of the ppl-pilot.com recommended it on the website (easier circuit to start with and gives a good way to test the controller). I spent about 2 or 3 nights working on it, building the circuit board, preparing the enclosure, and making sure it worked on the system. Having soldering experience helped, since I had quite a bit of components to solder and had to do a little bit of desoldering as well.

Next was the SNES controller. I worked on it for about 2 weeks, cleaning and preparing the controller, creating the circuit boards, the soldering, and making sure everything fit. It was definitely one of the harder parts, due to all the stuff to put into the cramped controller shell. A couple tries and I got it to work on with the receiver. I remember the good feeling of first playing Act Raiser on Virtual Console with it. It's definitely a great feeling to see something work nicely that I built myself.

I did have some debugging to do to the receiver, mainly since I did not put the best wires into it. After a month of working it out, it consistently worked well without error.

Usage:

As ppl-pilot.com describes, you plug the receiver into the GC controller port of the WII system. There's an LED light on top that shines red when it is on and turns green when it is receiving a signal from the SNES controller transmitter. The programs for the PIC's put into the receiver and transmitter assign the buttons such that they correspond exactly to the SNES controls for the Virtual Console games. For GC games, it loses the C stick and the control stick.

Pros for the controller:

1. Good Range - Same as wiimote.
2. Extremely long battery life - it uses an ipod mini battery, which has a lot of stored energy for the controller, which hardly uses any at all. I've played about 40 hours with it since March and have not yet needed to charge it.
3. Fairly light and compact - No wires to worry about, only slightly heavier than a normal controller, due to the added components. The receiver is pretty small and depending on how long a person makes the cable, it doesn't clutter the system up.
4. Perfect feel - playing the SNES VC games with an SNES controller feels awesome.

Cons:

1. Takes some time/experience to build - prepare to get frustrated with debugging of circuits. It's a part of building electronics. Also, if you are not careful, you can get some nice burns from the soldering iron or hot solder.
2. Lack of control stick and c stick support makes it incompatible with some games - First, the game needs to be compatible with the GC controller. Second, it needs to be able to be played without the control stick and c stick. That takes out a lot of WII and GC games. For instance, I had the intention of playing Super Smash Bros Brawl with this controller, but I can't remap the movement from the control stick to the control pad in the GC controls.
3. Signal interference can occur once in a while - it may be due to how I built the controller, but once in a while, a bunch of random buttons are pressed without warning. For example, I was playing Castlevania IV and paused the game for a sec, leaving the controller on as I ate some lunch. A couple seconds later, the game automatically unpauses and repauses 3 times and Simon whips and jumps a few times. I have no clue what it is, maybe some noise from the nearby laptop, some other signals in a neighbor's apartment interference, or just some errors in my construction. Doesn't happen enough to be too annoying, but sometimes it hurts.
NOTE: There was no mention of the signal interference bug on ppl-pilot.com, so his probably doesn't have it. If you build/have built this and do/do not experience this, let me know.

Overall:

Making the controller was tough, but it works well enough for me. There's still a couple existing bugs in my controller, but it works great and I am very glad I built it.

Alternatives:

There are some alternative ways to get an SNES controller for the WII that do not require soldering and thus a lot easier:

1. Nintendo Club Super Famicom Classic controller. This is basically a working Super Famicom controller that connects to the wiimote like the classic controller. It's not exactly an SNES controller (X and Y buttons are not concave, different colors), but its definitely a cool alternative to the classic controller. You can find it on ebay for about $40-110 dollars.

2. SNES to GC plug adapter. Basically a cable that connects any SNES controller to the GC controller port of the WII/GC. Very nice to be able to use your old SNES controllers again. Also, this is probably the least expensive option, costing only 19 bucks at retrousb.com (without shipping) to order. The only caveat is that you have a wire to worry about still. Then again, if you have an SNES controller, you should be used to it.

Conclusion/Thanks:

Thanks to the creator of ppl-pilot.com for creating his designs for this hack and for publishing them on his website. I hope this helps if you desire to try this out sometime for yourselves.