Although I have contributed to this thread, I don't really feel that LMDE is "unstable" as such. I have, however, experienced a few buggy situations that have been pretty much absent from the Main Edition (Ubuntu-based). If you are looking for a more trouble-free experience, I would recommend Main Edition over LMDE. I think the LMDE Debian universe is a little more wide open, and that brings with it both advantages and disadvantages. LMDE may be a little bit faster because it is unencumbered with the very code that eliminates the last 2% of the potential errors. There will always be questions about exactly which repositories to use, even among fairly well-informed users. I like to tinker with things, and I can dig pretty deep with a little bit of online guidance, but I don't care to have a system that doesn't always boot through to the desktop from the GRUB menu. When I do need advice and assistance, there is more available for the Main Edition (Ubuntu) than there is for LMDE. An Ubuntu-based distribution has the advantage that just about any worthwhile advice at the official Ubuntu forums will apply. While Ubuntu is Debian-based, LMDE and Main Edition don't seem to always have the same programs running in the background, and command line instructions that work for Main Edition (that is, Ubuntu) don't necessarily always work in LMDE.
For me, the advantages of Main Edition outweigh those of LMDE, and any difference there is in performance is just about unnoticeable. If or when Main Edition ever switches from Ubuntu-based to Debian-based, I am sure that it will run flawlessly because it will have had the full attention of the Mint developers. LMDE is an excellent distribution. If I like Main Edition 100%, then I like LMDE 98%, so let's not get upset. I'll still stick with Main Edition as long as it doesn't upset the entire applecart like Ubuntu Natty has done.