Include fields from the record in the Email that is sent out?
You can include fields (or columns) in the Subject and Message by using the syntax [Field Name] as described here.
Ensure email reminders are only sent out for Tasks are not completed or Issues that have not been closed?
The key to using SharePoint Reminder flexibly is to understand how SharePoint Views work. Task lists have a built in "Active Tasks" view that only shows tasks that have not yet been completed while Issue lists have an Active Issues view that only shows Issues that have not yet been resolved or closed. When configuring SharePoint Reminder you can choose one of these views as shown in the Tasks due and Overdue example.

If you have more complex requirements you can create a custom view that meets your needs. Review the Helpdesk example for a view that shows only High Priority active issues. You may also find the Create A View FAQ useful.
Not send email alerts for old items?
There are two ways to do this described here Tip - don't send Reminder email alerts for old records.
Only send email alerts for Modified items?
This page will help Tip - only send Reminder email alerts for modified records.
Pick up someone's email address from ... ?
Please see the separate Email Addresses FAQ.
Let users configure their own reminders?
SharePoint Reminder can only be configured by someone with "Web Designer" or "Administrator" permissions (i.e. someone who has permission to modify a shared page).

It is designed to be setup by one person on behalf of a group of people rather than by the individuals themselves as is the case with SharePoints built in "Alert Me" feature.
How can I temporarily disable a Reminder Web Part?
You can set the Resend Email to 0 times to temporarily disable an individual SharePoint Reminder web part.
Upgrade to the latest version of SharePoint Reminder?

To upgrade your existing installation without losing any existing web part settings :-

First remove the existing SharePoint Reminder by using Add/Remove Programs

Install the new version

Issue an IISRESET command (Start > Run > IISRESET)

If you are running SharePoint from a SQL Server database or have otherwise set the SharePoint Reminder Service to run under a domain account then please change the service "Log On As" account.

Tell which version of SharePoint Reminder I am running?
Open Control Panel then Add Remove Programs. Find SharePoint Reminder and then select "Support Information". You can check the version number against the revision history.
I can't work out how to get it to do what I need?
Contact support @pentalogic.net with a description of what you want to achieve and we will do our best to help!