I almost always return my shopping cart to the corral. I don't want my car hit by a randomly rolling cart, and I'd like to think no one else does either, so I don't mind walking a few extra feet to safeguard against it. Sometimes it's a fun game to test your aim and see if you can roll it in from some distance (with no other cars in the line of fire, of course).
As for tipping...
I worked for about two and a half years serving tables while attending physical therapy school. Gave me a whole other perspective on the job and what goes into it. I made $2.13 an hour (as that was the going wage in Utah ten years ago, who knows what it is now...), and if it wasn't for tips, I wouldn't have survived. I never saw a dime of those wages as the taxes on claimed tips wiped them out, and as a result, the amount on the pay stubs was $0.00 the entire time I worked there (with them watermarked with "This is not a check." No shit, thanks for the reminder). Once in a rare while, I'll still have a nightmare about serving tables where nothing gets done, and orders are piling up from pissed off customers. Point is, it's hard work, and even just adequate service will net you at least 20% in a tip with me if I'm dining at a restaurant. Subpar is usually 17-18%, and you really have to fuck up or ignore me to get a tip 15% or less.
That said, I only tip three types of people: Restaurant servers/bartenders, pizza delivery drivers, and barbers/stylists (and that last one is only because it's supposedly a rule and we should do it?) If you make my coffee, make my sandwich/burrito, fix my car (that was really there, Herrick? Are you fucking kidding me?), etc., (basically do what you're paid your wages to do), you're out of luck.