I'd do it, no problem.
Barbacks are the unsung heroes in bars. I loved bartending and had a phenomenal barback, he made my job easier and made it so I did my job better.
Keep a smile on your face, keep empty glasses and bottles off the tables, clean dishes as needed, cut fruit as needed, get new bottles when liquor runs out, tap new kegs, etc.
One bit of advice, ask people if you can get their empty glasses and bottles out of their way before you just go grabbing everything on the table...some people still have a few sips of beer left, or want to chew on the ice left in the glass, etc. and don't appreciate their table being bussed before they're ready, and it will hurt the bartenders' tips, and therefore, your tips.
And to answer your actual question, it can be easy if you have the right attitude going in. I'm sure you'll be busy and that can be stressful. Know the lay of the land, and the area you're responsible for. Keep a steady eye on your area and make sure you see needs as quickly as they happen. As a barback there is typically always something that can be done, don't think you've finished working just because the tables all have full drinks.
Make sure your bartender is happy. I always tipped out my barback more than standard percentage, because I never had to worry about anything more than making drinks and keeping customers happy, and he just covered everything else.
[This message has been edited by Maia Nyx (edited 1/28/2011 2:38p).]