How reliable is the company you pay to host your domain's Web site and e-mail? NetWhistle's PersonalWhistle will tell you. This free monitoring service pings your Web site at fixed intervals to see if it's up. It can also check e-mail boxes at the same intervals. If there's a problem, the service logs it and notifies you via e-mail (or by pager, if your paging company has an e-mail gateway); it also delivers a weekly report card. The service will monitor up to five URLs or e-mail boxes at specific intervals; to either monitor more addresses or monitor at more-frequent intervals, you'll have to pay.