A few of us have spent much of the weekend exercising the FSQ system on 40 metres. Here are some preliminary thoughts. During our tests we only used some of the FSQ facilities; for example we did not try its Fast Simple Messaging protocol. Note that I am not an expert on FSQ so I may have some things wrong, if so let me know and I will correct them.
The mode itself seems to work fairly well although without any error correction, errors at weak signal levels are quite common. In the face of co-channel QRM (specifically RTTY), FSQ performed poorly; in fact it was largely unusable. It was also unusable if two FSQ stations were transmitting at the same time - working with stations in and out of skip meant that unintended collisions could occur despite the squelch hold-off facility. [note FSQ does have an error correction system for file transfers - this is separate from the standard QSO mode].
The system functions are quite novel and mostly seem to work as expected. However, the lack of error correction discussed above means that they do fail quite often. The "relay" facility is interesting but effectively halves the data rate as the channel is used twice for each message.
The slow data rates mean that sending large amounts of data is impractical; think "tweets" not big text files. The designer of FSQ suggests it's similar to sending an SMS text. Radio-preppers would find it usable for short sitreps (using the associated Fast Short Messaging form system perhaps).
The ability to automatically request a signal report from another station has all sorts of applications but it did fail sometimes with the report being sent as snr=-nan db.
The image facilities are novel but do need far stronger signals than the FSQ itself. Thus, even if you can initiate image sending from a remote station, the results can be disappointing.
The channel sounding facility is useful as it enables stations to build up a picture of who is on the channel. If there were ever lots of stations it could cause a significant drop in channel data throughput.
The "heard" list has no way to clear it beyond restarting the program. This is troublesome as the program does not recall some settings so they have to be reset each time. Also the heard list gives no indication of when the station was last heard so you are left with old entries for stations who may well be long gone.
It appears that hardly anyone is using FSQ in Europe. Few stations were seen outside of our experimental group. I am told that leaving an FSQ RX on 7104 kHz overnight will yield a few more DX calls.
...all that being said, I did enjoy using FSQ as it is better for a slightly more relaxed keyboard chat than most other data modes;no brag files here. It's clearly a work-in-progress and I'm looking forward to seeing where it goes.