MRing is a bit of a hobby for me. Some is paid for by my employer (but not much), some is tax deductible for certain reasons etc, but both those combined would be less than 10% of my travel. This year it was probably 5%
Using creative skills to find cheap fares is fun, and I enjoy the lurks and perks of status with airlines/hotels etc.
I spend way too much on the hobby, but some people collect vintage cars, some people hire yachts or compete in yacht races or spend thousands on dirt bike rallying or dvd collections they never watch. I choose to travel, and for those people I just think they have a different view on life.
I have learnt lots by travelling and seen some unique (and too touristy) sites. Have had some bad moments, have had some good moments and some excellent moments.
Highlights like a rare upgrade to BA F (from a J award) was nice, so are the suites and executive lounges I've been in at certain hotels when I've paid a very low rate to start off with.
Airport lounges rate from poor to excellent, and places like the HKG Cathay Pacific F lounges and the Sydney/Melbourne Qantas F lounges are a very nice place to while away spare time before flying.
Bad moments include lost baggage, missed connections and lots of stress at various times from risky trips and suspicious customs officers. I've also become sick a few times from the travel I've done where I've picked up infections during my travel (colds, flus even chickenpox!). I also feel like I sometimes no longer appreciate holidays like I once did, and won't spend the preparation time I used to on a trip, and for some reason find flight after flight trips more interesting than direct (eg adding an additional 5000 miles (50%) and 2 sectors onto a UK trip by finding a way to go the wrong way around)
It's also the little things, for example with Qantas, I can't remember having a middle seat last year and about 80% of my domestic trips had a spare seat next to me (and were in rows 4-10). Being able to choose seats before I travel on Qantas Internationally also allows me to get my preferred seats (middle aisle).
There are people who don't agree with MRing here, and others who are concerned about the greenhouse footprint of the 'excess' travel. Similar to my comment above, very few people know my personal circumstances and they should not be throwing stones themselves.
The other thing to watch is that status is easily diluted by airlines/hotels etc, and there are so many 'elites' in the marketplace that getting some of the listed benefits are hard. Plus the constant battle to try and work out if a 45 min connection at some weird airport in the US is achievable or not

or why you should change hotel after your first night!
PS - Virgin Blue Velocity (I assume that's the FF scheme you were referring to when you discussed 600 points?), is not an easy program to MR with. The non-flexible points system ensures that you pay fixed amounts for travel to get status within Australia. I am yet to analyse overseas flights, but there may also be some bonus partners that could assist with getting status (but once again, I've not researched it thoroughly)