I have a horrible commute everyday into work. M25 and A1... Sterling to Apex - anyone who lives near enough to London will have heard it on the Radio everyday.... Sterling and Apex are roundabouts on the A1 about a mile or two apart and the traffic is always crawling between the two. In the car it takes about 20 minutes or so to get between them. This is the reason I bought a scooter.... so I could filter. It really is the only way to move sometimes!
To be honest the scooter i have isn't great for this as it's a big "mutha". A yamaha majesty 250, quite wide and the A1 lanes are NARROW, making filtering just that little bit more scary. Most drivers are courteous, and I usually pass through slowly although sometimes you do have to give it a bit of acceleration to make damned sure you clear the gap before the cars start moving again. It stresses me out quite a lot, and I'm slower than a lot of other bike riders, so I let them pass me if I can. However it cuts at least 10 minutes off the journey time and I'm not just another cage making the queue longer!!.
Filtering on the M25 isn't so scary as the lanes are much wider, I also only filter if the traffic is doing 20mph or less and I pass at 20mph or less faster than the cars are doing (I found a good website which gave some pointers for "safe" filtering. I would never filter at speeds higher than this although I regularly see crotch rockets and sometimes RAT bikes "filtering" at 80mph plus in traffic moving at 70mph... nutters.
Oneday I was sailing along a gridlocked M25 which was parting like the red-sea in front of me.. "weird" I thought "there's usually space but not normally this much" As i got a mile or two through the traffic I found out why - a BIG massive new Goldwing was filtering through the traffic... and you could see the scared faces on the car drivers when they saw THAT in their mirror!!
Mr Goldwing let me pass though as he really did need a lot more space than me - suddenly my Majesty didn't seem so large any more!