I've had 3 diversions. 2 were due to medical emergencies [made unscheduled landings to allow medical people to remove an ill passenger], the third was more involved:
Flt. AA44 on 1/12/14 from LAS to JFK departed on time and (due to tailwinds) was now scheduled to arrive 30 minute early. About 90 minutes from JFK, due to weather and mechanical issues (at JFK), the flt. was in a holding pattern (expected to last 30 minutes)--but that stretched to 1 hour. The plane was now being diverted to SYRACUSE, NY. After one hour on the ground (plane had to be refueled), the fight was to take 40 minutes to JFK; BUT (JFK still had problems), 30 minutes from JFK...a new holding pattern...there was a NEW diversion possible [not enough fuel was added at SYR]. Finally we received clearance to land at JFK. 4 HOURS late--but at the gate we had to wait over 10 minutes for them to find a GA.

3) US express flight DCA-MSP diverted to PIT with "landing gear sensor error" - all was fine and we were on the ground just over two hours.

In my past 4 years of heavy flying (100k domestic miles a year or so), I've had one diversion. Happened a few weeks ago flying LIT-ATL. Were 20 mins into the flight when we turned around to go back to ATL. Hit a bird on and it had damaged the front landing gear doors so they wouldn't close.

Multiple medical emergencies in the air, but all were resolved in the air and we continued on.

Twice for me out of around 450 segments:

1) March 2000 AA SJO-MIA diverted to GCM after the fuelers in SJO went on a wildcat strike and necessitated an enroute stop to take on more fuel.

2) May 2006 NW BKK-NRT diverted to HND after high winds at NRT meant a long hold which eventually resulted in a diversion

I've had two diversions in ~6 years of business flying:

1. B6 JAX-JFK: Took off slightly late, and were in a holding pattern due to ATC Delays in to JFK. Pilot announced we were going to land at ACY to refuel and continue up to JFK. When we land, one person was not feeling well, so an ambulance was called. Then we find out the pilots timed out. Luckily, a deadheading set of pilots were on board, so they flew the ACY->JFK leg. Got home at 2am as opposed to 9pm.

2. AA DFW->LGA. Some bad weather or something in LGA, so we ended up landing at BWI. We were there for like 45 minutes or so. I told my boss(as a joke) that if I wanted to have a layover in BWI, I would have flown WN.

forgot one

Nov 79, on a NW 747 inbound from HNL ... we shot two approaches in the fog at SEA, and put down at BFI where they had buses waiting to take the 300-some pax and their bags the last 5 miles ... scheduled arrival was around 830pm and I think we got to SEA ~11

a friend of mine was not so lucky ... she was on the same flight the next day and they landed in PDX; the buses got to SEA about 2am

Never had any diversions, then had two within three months this year. First was flying FLL-MDW. Snow in Chicago caused a brief (~ 45 minutes) diversion to SDF. Second was BWI-ISP. When we got near ISP it was too foggy to land, so we circled a bit. Then the minimums came up enough for us to try to land, but the fog had other plans, so we went around (another first, but OT here) and diverted to PVD The weather at ISP cleared shortly thereafter, so we were only on the ground for about 1/2 hour. Given how bad diversion delays can be, these were probably about as small as possible.

In 1K+ flights only two. TATL flight JFK-AMS turned back to JFK after mechanical on 2 of 4 engines. One DFW-ORD flight diverted to PIA for snowstorm at ORD.

Never had any diversions.

I did have a close call after Departing Melbourne to Sydney then Vancouver. About 15 minutes before our landing time there was an announcement that we may need to turn around due to fog at Sydney. What a nightmare. I thought the flight is long enough without adding an few hours. Luckily for us 5 minutes later the pilot said we could now definitely land! Yeay!!

I actually had one I was PRAYING for a diversion. 1 hour in to a flight from Honolulu to Sydney where there was a fire on board and we were sitting in pitch darkness with the stewards running all over the place. Pilot finally announces that we have had a fire and it looks ok. I wait for him to say we are turning around... instead he says we are continuing on to Sydney... 9 hour away! God I a glad to land!

Once a diversion, flying LCY to RTM. Heavy fog over RTM, circled 3 hours /for a 45mn flight) and at the end they decided to land in BRU as the plane was low on fuel. We learned later that if they had waited 5mn we could have landed in RTM. Instead of the plane taking off again to RTM, we were bussed there...

SFO-LHR diverted to Gatwick due to weather and traffic. A more exciting one happened to a Czech friend on a package tour charter from Prague to Mombassa. They diverted to Sana'a, Yemen and were not even told where they were landing. That was due to a MX issue and they were on the ground for about 12 hours.

Only 1 diversion in about ~500 segments or so lifetime...DL CVG-MCO a few years ago diverted to ATL for a medical emergency....

Twice for me in the space of about three years...

CBR-TSV diverted to BNE due to technical problem with the aircraft.
LHR-SIN diverted to DXB due to medical emergency.

I've been a regular flier for 25 years, probably averaging 30-50 segments per year, and I've never been diverted. Nor can I think of a time that someone who was coming to visit me, or flying to meet me at my destination, has been diverted.

On the other hand, I can think of probably 10 times when my flight has been delayed or cancelled when the inbound aircraft was diverted.

Reflecting on them, those numbers seem odd.