My Paypal acct has been backed by my checking account from the beginning. It only draws from your checking account if you don't have enough in your PayPal account to cover whatever it is your buying. Plus, it only deposits to your checking account if you "withdraw" the funds from your Paypal account. For instance...

Say you sell a chip and are paid via Paypal for $10, $10 goes into your PayPal account (and sits there until you withdraw it). Say the next day, you buy a chip for $8. Your Paypal account will have a balance of $2 now. Now say you buy a chip for $20 - now I'm not so sure if it withdraws the full $20 from your checking or if it uses the $2 in your Paypal account and only withdraws $18 from checking, but the point is, it will go to your checking account to get the funds it needs to complete the transaction.

Hope this helps,
Will