If I go with a Lithium Polymer battery, will my 5 amp GWS ESC for my Slow stick cut off the juice to my motor at an appropriate time to avoid overdischarging and ruining my batteries? Should I invest in a castle creations programmable ESC before even attempting to fly with a Lithium pack?

Thanks

I fly this combo all the time, No The Ics 100 ESC will cut voltage between 4.2-5volts. This is what I have seen on my 3 during test runs on the bench. I fly a 2c pack which doesn't need to be discharged below 6v. I time my flights to make sure and stay over this. You need to check the voltage under load also, If you fly and then check the voltage it may have come back up to over 6v but could have been below that under load. The only way to do it is time it. The bench runs are a very safe way to do it. If you get 12 min under full load to reach 6v then a 12 min flight under flight conditions will be over 6v. Hope this helps
Brandon

I wouldn't worry about voltage cut off. The GWS ESC will be fine.
The reason being that your plane simply will not be able to stay airborne at 6.5 volts or less unless it is a powered glider or something.
I've been running LiPo's in all my electrics for a while now and have never had a problem with too low of voltage. When the Lipo's fade, they'll do it fast and you'll be able to tell right away. Run your timer and you'll get a ballpark idea of how long you can fly. I think the lowest I've ever run a 2S Lipo pack down was 6.3 volts under load. That was on my MiniSpeedwing.
I caution against extended bench testing electrics. Sustained static loads are hard on your motor and ESC. If you must static bench test, keep runs as short as possible.
Once you go LiPo, you'll never go back !

I was told today by my local Hobby shop guy, that I would simply be unable to use lithium poly's in a slow stick because the current draw was too much and would ruin the batteries. This is certainly the first I have heard of this. Is there any truth to this?

Depends what Lipo you want to use.
You couldn't run a 2s 1020 kokam. A 2s E-tech 1200 would work, but it will push the cells a little hard. I wouldn't fly the plane for extended periods at full throttle with the latter.
You could run a 2s2p kokam or the same in E-techs. They could handle the amp draw and give you really good flight times. I prefer to buy my cells ready made in the 2 series configuration. Then I just make my own Y harness to run them in parallel. That way I can break the packs up and run them in planes that don't require that high of capacity/discharge. In parallel you'd have 2040mah and 2400mah capacity respectively. Drawing 7-8 amps you can see that flight times would be long...and if you throttled back just to cruise around....flight times would be really long. Just guessing, with parallel packs, you'd be around 40 minutes flight times at about a sustained 2/3rds throttle. I wouldn't be flying electrics if it weren't for Lipo's. I hate charging batteries.
Check this forum and the battery forum over at the e-zone...good info. A little research goes a long way. Hope this helps.

What about the packs sold at radicalrc.com? I am a little confused by the different brands.

I'm pretty sure Dave's cells are kokams. The 4 cell pack would work in the SS. I think it's 54 bucks with connector. Remember you'll need a Lithium specific charger as well. It's an investment getting into Lipo's-which I feel is worth it. You just have to decide how far you plan to go with the hobby I guess. Dave's a good guy to deal with. Here's a few other links though for more options. I've shopped with all of these businesses and wouldn't hesitate to do so again. I have to stress to you to do a little research on Lipo's. It'll really help when trying to decide what route to go.

http://www.lightflightrc.com/

http://www.b-p-p.com/etecpremade.htm

I have done some research, but obviously I need to do more. I definitely plan on being in the hobby for a while. It's a blast. I currently only have 3 batteries and a charger, so if I head into Lipo now, I would be in good shape I bet. I was looking at getting the plantraco charger for the Li's. Thanks for all your help.