So, I have been playing in a band now for about 2 years, and people are starting to hire us for parties and such. I have thought about getting a wireless input system for a while now, but now, it seems as important as ever.
My questions are: Are wireless input systems reliable enough to play for a few hours at a time? Am I better off with the old fashioned way of a cable? if I plug in the other end of the system (the Receiver) into my pedal board, will the system still work? All help is appreciated.
The professional-level systems are, of course, very reliable.

And yes, you would plug the receiver into the beginning of your pedal board.

I wouldn't spend less than the cost of the Line 6 G30 to buy one, however. In the past, the rule of thumb was "plan on spending about $500 and make sure the brand name is Shure." That's gone by the wayside a bit since Line 6's digital series wireless pretty much ate Shure's lunch.

The G50 by Line 6 would be my baseline recommendation at this point (I have the rack-mount series that uses this same transmitter), though Shure has recently introduced its own digital that's very good, and in pretty much the same general price range.

One caution, however. I very much dislike having expensive electronics (and particularly those that use AC power) out front at any gig where there's a chance of an audience member or an over-enthusiastic (or bouncy) band member can physically impact them or drop adult beverages or any variety of bodily fluids on them.
Line 6 G50

Reliable? Yes
Better off with a cable? Only if your boring and stand still. Then i wouldnt buy wireless unit. Use a cable.
Where to plug in? Begining of you pedal board. You can buy pedal board transmitter or a rack mount reciever.

Your better off with the G50 (as far a durabilty and range) but dont buy anything less than the G30 if your hurting for cash.
I've got a Line 6 G50 that on fresh batteries will last 9 hours.

It's been reliable so far. Sounds as good as a cable to me. Lately I haven't been using it though. Just one less thing to bring.