Slightly late to join fMMS bandwagon but here's my feedback:

fMMS version: 0.2.8
Network: T-Mobile UK
Settings: http://wiki.maemo.org/MMS#T-Mobile_UK
MMS out test: works OK, generally, ie. picture gets through correctly, but on wife's phone (Sony Ericsson S500i also on T-Mobile UK) I get following message instead of text:

MMS in test: works also OK, I get both text and attached picture through correctly, but under the message I get "AAAA" button which does nothing. :-o

Other notes:

• fMMS should handle errors better. For example, when I tried to send a message initially, I've got notification about resizing image that got stuck for quite long. In the meantime I realised that I'm connected via WiFi, not GPRS. I connected, but fMMS was still stuck on "resizing image". I've had to kill it and once retried - image got resized and sent instantly.
• I also have intermittent trouble opening incoming message, ie. fMMS gets stuck when "attempting to download MMS" and I have to kill it and retry again, which usually works fine.
• "T-Mobile MMS" settings are exactly the same as "T-Mobile Internet" APN (for accessing internet generally) with only difference of proxy address, which is not present in "T-Mobile Internet" profile. What is funny tough, that I don't necessarily have to connect manually with "T-Mobile MMS" profile, as connecting via general "T-Mobile Internet" works just fine for MMS too (despite of having "T-Mobile MMS" profile selected in fMMS options).

Sorry in advance if I re-iterate issues that possibly were discussed before, but getting through 48-page thread is somewhat troublesome. :(

That's about it, so far. Despite few inconveniences, fMMS actually does the job and that's great - well done, frals! Since Nokia itself is offering support in fMMS development, I strongly believe it will shortly get very close to perfect solution for seamless MMS support in Maemo as a whole! Actually, I think it already is quite close, but would be much closer if it was integrated with Conversations. :)