I'll try to keep this short:

I was a bit obsessed about this a few years ago, and I still have over 15 sets of cranks, ranging from 165 to 177.5. I'm 6ft with long legs, and I persisted with 180s for probably a bit over a year (I think in 2003/2004). I loved them at first, and thought I had a 'secret weapon' but then they started to annoy me after about 6 months, because I felt like I couldn't "get on top" of the pedal on the start of the downstroke, especially on longer rides on flat roads. I kept wanting to get off the saddle to compensate for this feeling.

I'm not a sprinter, so cadence never bothered me with long cranks.

I eventually started experimenting back on my 175s, and 172.5s, and found that I felt no slower with these shorter lengths. I also found I could get more much aero (lower upper body) on the shorter cranks, because my thighs weren't hitting my stomach (there's a whole 'thing' going on in the tri world at the moment with John Cobb getting everyone super-aero on 165s, coz they can get way low).

I continued switching between the different lengths for a couple of months, then, after having one particurlarly awesome ride on 175s (and after some persistent medial knee pain), I ditched the 180s. This meant that I needed some more shorter 7800 Dura-Ace cranks, and my local second hand store did a good price on 2 pairs of 172.5s, so I settled for that length. I probably would've been just as happy with 170s or 175s. So, now I ride around mostly on 172.5s, and sometimes on 170s, and i don't feel any slower. I've had a bit of a knee injury lately, so I sometimes roll around on 165s, which reduces the flexion at the top of the stroke.

One thing I did really like with 180s was that I felt as though I had more power when stomping off the saddle when riding over short hills, and bridging gaps, etc, (darting out of corners) in criteriums. So, I did sometimes miss the 180s for this, especially in hard criteriums on wind-effected courses, so I went and got a couple of pairs of 177.5s. I sometimes race on these, and occasionally take them to the local hilly group smash-fest.

Anyway, having said all that, you might like 180s -- a lot of taller guys do -- so I figure they're worth a try. As the article in my previous post says, the issue is more complicated that just "leverage vs cadence, with some positional things thrown in".

Also, there are some logistical issue when using longer cranks, especially if you have big feet and ride with your toes out/heels in. Some dudes have problems with their heels hitting the stays, and even (rarely, maybe) the rear derailleur. Long cranks also (obviously) reduce pedal ground clearance when cornering. And, depending on your bike, your toe might hit the front tyre.