If you buy stock on margin the broker holds your stock as collateral and can loan your stock out. But if you own it free and clear you don't have to leave it in the account.
With respect to the "tax thing" go to www.irs.gov and look at Form 1099 MISC, box 8. When your stock is loaned out, and you receive "payments in lieu of dividends", this is the form the brokers are required to give you. These payments are required to be reported as "other income" on your tax return. Not as dividend income. You don't get a Form 1099 DIV.