Just twice for me, once on PC on normal and once on 360 on insanity. 
 
Soldier first time, Infiltrator second. Do you think the classes have enough variety to make each playthrough feel somewhat fresh? 
 
My second playthrough felt really fresh because it was almost a year after I finished the game the first time plus I bought the 3 mission packs. (Kasumi, Broker, Overlord)

Just once as Vanguard. I plan on playing it through it again just to play the DLC missions, in particular the Shadow Broker one. I beat it within 2/3 days of its release so my second playthrough will hopefully feel like a whole new experience. It won't happen for a while however, I'm currently playing through Mass Effect 1 again making a few different choices this time around to alter ME2's plot.

Twice. Both as soldier.

Only once. Not only would it be a hassle to play it again (since for my first playthrough I borrowed it from a friend), I also didn't particularly like it the first time through anyways.

Thrice, gonna be 5 when I get it back from the friend that borrowed it.

Twice.

Four times for me: two playthroughs with my main paragon male Shepard, one playthrough with my main renegade lady Shepard, and another one with a paragon lady Shepard. I need to finish a renegade male Shepard playthrough now :p 
 
Edit: also I think playing the different classes will probably feel more different in higher difficulties. I've been playing vanguard, adept and soldier so far but only on the normal difficulty, and they don't feel terribly different.

twice

4, going to do another before ME3 probably.

" Thrice, gonna be 5 when I get it back from the friend that borrowed it. "

3,  male, female, and hardest difficulty playthrough's

Female Adept Hardcore
Male Vanguard Insanity
Female Infiltrator Hardcore
 
That's nothing compared to my 26 ME1 completes :/
Now I'm starting to doubt if the game really was that good xD

Twice. Once on the 360 and another on the PS3. Now if Bioware will fix the game+ glitch then it would be 3. 

5 times I believe. 1 soldier, 3 vanguards, 1 adept. 
 
4 times were female. Jennifer Hale all the way. The only reason to play Male Shep is Tali. 
 
1 time was on Insanity as a female Vanguard.

Three. 

" Three.  "

" @Geno said:

" Three.  "

Say thrice goddamnit! "

My main character is a good male Shepard, and I quite enjoyed playing as a Vanguard.
 
I'm about halfway through with a renegade female Sentinel, but since I did most of the side stuff on my first save, things are getting kinda tough as I critical path my way through.

" @CL60 said:

" @Geno said:

" Three.  "

Say thrice goddamnit! "

Thrice! "

Four times -- Infil, Vanguard, Soldier, Sentinel (on insanity) in that order. I'm working on another ME1 save to import into ME2 for my refresher before ME3 -- stupid shadow broker dlc ruined my s-rank though! >.<

Twice, once as a paragon soldier on normal, and then a renegade adept on insanity. 

I think just twice.

Six times in total. I have five Shepards, but one I played through with twice: one for his initial soldier run (which I hated), and another for my eventual Insanity run as a Sentinel (which I'd take over playing as a soldier on a lesser difficulty any day)

Twice. Played the first time with my paragon save on pc and immediately on completing that I started again on my Renegade save on pc. I completed the game twice in under 10 days, the first time I've ever played a game again immediately after I finished. And I have to say, Renagade was more fun.

 Twice. Both as soldier.

seven or eight times. I love mass effect.

I've lost count, six... maybe seven times? 
 
I kind of got super obsessed with the game for the first half of last year. I stopped play for I while but with all the GOTY talk that happened last month and the ME3 announcement I find myself hooked all over again. DAMN YOU BIOWARE! DAMN YOU FOR MAKING SUCH AN AMAZING GAME!

I think about ten. 8 times on PC with varying difficulties then twice on 360, Veteran afterwards Insanity. Hell, I'd do it again.

Only twice, both times with soldier. Have to try out those biotic classes third time around.

Too many time, at least once with every class and every time a new DLC is released I restart.

5....

" @Geno said:

" @CL60 said:

" @Geno said:

" Three.  "

Say thrice goddamnit! "

Thrice! "

Thank you. "

Just the once.  I usually don't have time to go through story games more than that.

Twice... but perhaps more telling is that my wife beat it twice, and she's never played or beat a video game before in her life.

To completion, twice. I got halfway done another three times.

Once, got tired of it during my second playthrough.

No less than 10 times, but on a total of five characters. I'm very picky about getting my decisions the way I want them.

" Twice. Both as soldier. "

ME2 twice, ME1 quice. Hopefully I'll keep this mathematical trend going and only play ME3 once. Actually that would be tragic depending on how the game is   
 
ME2: Infiltrator, Adept 
 
ME1: Infiltrator, Infiltrator (Same guy for New Game +), Adept, Vanguard
 
btw quice = 4

Once with 2x midway games going currently.

I completed it once, The first Mass Effect I completed about 5 times. Something about the first made me want to replay it more. I think it's because of the RPG elements it had? Anyway I see myself beating Mass Effect 2 once more before the 3rd comes out.

I'm only midway through my second, &purely to get a save I'm happy with for ME3.

Just the once. Both Mass Effect games are my mates so I did my one proper play on both so I can carry over into the 3rd.

Twice, probably going to try and run through another time with a female character on easy, just to try out more classes.

Just once. As much as I love the game and the series, I can't get myself to play through them again for some reason. I've never been a fan of replaying (except chrono trigger, which I replay biyearly).  
 
Which is weird considering I routinely watch the ending and trailers on youtube and I still love them.

5 times after its release. A couple more times during development.