Users new to CompuServe forums are often perplexed by a shorthand used by
"regulars."  Popular acronyms are in order:

BTW      - By the way
FWIW     - For what it's worth
GD&R     - Grinning, ducking and running
GD&R,VVF - Grinning, ducking and running, very very fast
IMO      - In my opinion
IMHO     - In my humble opinion
IAC      - In any case
IAE      - In any event
IDK      - I don't know
IOW      - In other words
JIC      - Just in case
LOL      - Laughing out loud
NBD      - No big deal
OTOH     - On the other hand
PITA     - Pain in the @%$
PMJI     - Pardon me for jumping in
PMBI     - Pardon me for butting in
ROF,L    - Rolling on floor, laughing
RTFM     - Read the fine manual
TIA      - Thanks in advance
TIC      - Tongue in cheek

  On our forum, moreover, even those "regulars" would be confused by many
acronyms which stand for rather professional terminology.  They include:
 
AAPB     - American Association of Psychophysiology and Biofeedback
AD       - Alzheimers Disease
ADD      - Attention Deficit Disorder
ADHD     - Attendion Deficit/Hyperactivity Disorder
BF/BFDK  - biofeedback
BMB      - Brain/Mind Bulletin
CAC-III  - Certified Addictions Counselor
CES      - Cerebral Electric Stimulation
CFIDS    - Chronic Fatigue/Immune Deficiency Syndrome
CFS      - Chronic Fatigue Syndrome
CNS      - Central Nervous System
DSP      - Digital Signal Processor
EDR      - Electro Dermal Response
EDS      - Episodic dyscontrol syndrome
EEG      - Electroencephalography
EKG      - Electrocardiogram
EMG      - Electromyography
FDA      - Food and Drug Administration
FFT      - Fast Fourier Transform
GSR      - Galvanic Skin Response
LPC      - Licensed Professional Counselor
MAT      - Mind Awareness Training
MPD      - Multiple personality disorder
MRI      - Magnetic Resonance Imaging
NDE      - Near Death Experiences
NIH      - National Institute of Health
NLP      - Neuro-Linguistic Programming
NREM     - Non-REM (rapid eye movement)
NSP      - Nadi Shodhan Pranayma (Alternate Nostril Breathing)
OCD      - Obsessive Compulsive Disorder
PAC      - Political Action Committee
PED      - Positive Experience Diary
PMS      - Premenstrual Syndrome
PNF      - Proprioceptive Neural Facilitation
PNI      - psychoneuroimmunology
PPG      - Photoplethysmograph
PSP      - Psychophysiogical Stres Profile
PTSD     - Post Traumatic Stress Disorder
REM      - rapid eye movement
RSI      - Repetitive Strain Injury
SFN      - Society for Neuroscience 
TMJ      - Temporomandibular Joint (jaw, usually refers to pain in that joint)
VTVM     - Vacum Tube Voltmeter