I am an experienced FL Studio user that switched to Linux about a year ago. I now use Ardour for  most of my recording work, but now that I have found LMMS, I would like to start using this, as it seems very similar to FL Studio (I last used FL version 6 producers edition)
I am also a fairly experienced programmer (though admittedly I don't have time at the moment to dive into another project).

That being said...

LMMS has had a very good first impression on me. I'm nothing short of amazed with where the project is right now, in such a short period of time. I'm also very pleased to see it is very FL-like, and that .flp file import is one of the features.

Now for some questions... (I searched the wiki but could not find much information on these...)
1) Is .flp import 100% working, or still in early stages?
2) I use an MAudio Delta 1010 sound card. Right now I have tried LMMS with ALSA only. But in the settings, I could not change the channels from the default of 2. Also, for each track, I could not find a way to associate a track with any specific output of my card. Any suggestions on how to best set LMMS up for my Delta 1010?
3) I tried using my M-Audio Keystation 49e keyboard with LMMS, but didn't seem to get it to work. Is Midi support fully working?
4) Can you record an audio track while playing back the project? (I just do acoustic and vocals really.. I add some synth stuff and drums via the sequencer but most of my work is based around recording an acoustic guitar, slicing up the different parts and re-ordering them to make the song track.. Then playing the song back while recording vocals...  Does this fit LMMS's capabilities?
5) I haven't had any luck getting .flp import to work. I am running LMMS on Ubuntu 0810 Intrepid on my master drive. My slave drive is my old Windows C: drive. In the settings I have set the FL Studio install path to /media/C:/FLStudio6 where the original FL Studio installation was, but that didn't get anything to work. Also, I'm confused on the VST path..  I'm on linux, so do I need to fill this out?

Next, just a few bugs I've noticed...
1) On anything complex, scrolling the song editor is almost impossible because it gets so slow and jerky
2) Maximizing the beat/bassline editor stretches the beat switches across the screen.. The desired behavior would be to expand to see more of it.

And lastly, some suggestions
1) Having a forum would help this project progress so much faster...  Nobody really does mailinglists anymore (and I know very few people who like them). It would also get more people involved to improve documentation. I almost didn't even check out LMMS due to the fact that there was no forum for support.

2) The wiki is very incomplete (see suggestion 1)

Overall, very impressive. I'd like to see this project progress very far, and even help out myself at some point!