2 basic Textmate shortcuts ‘don’t save’ and ‘replace all

"How do I press search and replace after the S/R dialog box is up? - if you press enter it just takes you to the next occurrence of the search string

The buttons in the box map to the same options under Edit > Find, so you can use those key shortcuts. So the Replace & Find button is ⌘+Control+F, etc. You can also use some of the other selection items in Edit > Find. For example, if you have a word highlighted, you can use ⌘+E to use that word as search text, and then ⌘+G to walk through occurrences of that word. You can also selected another word to use as replace text with ⌘+Shift+E, then step through the occurrences (using ⌘+G) and use Replace All in Selection (⌘+Shift+Control+F) to replace. All these shortcuts are listed in Edit > Find for easy references.

when I close a file that I don't want to save, how can I choose don't save without touching the mouse?

You can press ⌘+D as a shortcut for ""Don't Save"". Incidentally, this works in almost every document-based application on Mac OS X -- not just TextMate."