I haven't. I use it every day, for a number of purposes from updating my blog to working on the Woobius codebase (in both Rails and Flex/AS3), and I haven't had any issues whatsoever. The global search-and-replace works great, too.

I'd quite like split-screen editing, that's my main bug-bear, but I've actually structured my use of TextMate around that - I basically just have several Textmate windows open. I've been meaning to switch to Emacs for that, but I suspect that managing buffers (and making sure they end up in the right pane) will take as much effort as dragging a few windows around.

"but I suspect that managing buffers (and making sure they end up in the right pane) will take as much effort as dragging a few windows around."

I think you'd be surprised. In my experience I have a fixed set of windows (not os windows, but panes, as you called them), and easily and quickly switch between them with Iswitch-buffers: http://www.emacswiki.org/emacs/IswitchBuffers

this add-on gives you incremental-search to choose among open buffers, and usually it only takes a couple of keystrokes to get the one I want - so instead of moving the mouse around and clicking somewhere small and dragging things around, I am back in business after something like 'C-x b sh' - control-x, b to invoke iswitchb, and 'sh' to get me to my shell buffer...

The problem I think I'll have is not so much the actual switching of buffers, but making sure they end up in the right pane when first opened.

That's good — you've had better luck than I. It has crashed somewhat randomly from time to time for me, usually when I'm working with a lot of files or doing a search. Search works well for me, but it's sometimes slow and could be designed more effectively.

"Ack in Project" is so much better than the built-in search it's not even close.

Have you found a replacement for "jump to file"? Command+T is great until you have a lot of same-name files in different directories (it doesn't take the directory into account).

e.g. in a Django project it'd be common to have users/models.py, events/models.py, polls/models.py - you press Command+T and you can only search on models.py, if you type "pmod" you don't get polls/models.py. Highly annoying when hopping between files is so common.

No - it crashes less than once a month on my system and I'm using the excellent Ack in Project mentioned by others instead of the built-in search. The Project Plus bundle also gives a nice for large projects but in general Ack is the only one I consider necessary.

Not much, but yeah search does brick out occasionally and TM must be restarted.