I went through the tutorial, created a fighter (Jack Mayhoffer), and have been progressing through career mode. My record is now 17-3-0, all by KO or TKO...I haven't been able to land a single submission, even though my guy's submission offense is nearly at 70 now.

I'm able to do transitions and get into a good position, but any time I try a submission the computer just gets out of it and we stand up. I seem to win almost every fight by getting a lucky stand-up knockout, or getting into full mount and bashing my opponent's face in.

Any tips?

You and me both, I'm currently 18-3 now and all of them have been KOs. This isn't going to be a post that is going to help you, but I'm glad to know somebody is going through the same situation. The tutorial doesn't do a good job of explaining everything thoroughly, to say the least. As far as I know, I think getting into the submission (and a successful tap-out), is dependent on their stamina and how much damage they have sustained. I don't think there is truth to that, though, because my dude tapped out within a minute into the match, and sustained minimal damage.

I hate kicking and punching my way to wins, because I just want to get the Submission of the Night for one achievement.

Weird, I seem to be having the same sort of problem. My submission offense isn't nearly as high as yours yet, so I figured it must just be that, but I guess not. It could be that the guy's stamina was too high, as I never manage get it into the red before they get knocked out, has it been low when you tried the submissions?

MB:  amazing at SFIV, bad at UFC.  lol

turn the HUD and only attempt submissions when their stamina is low

Submissions against real life online fighters are easier, if not completely arbitrary.

Alright, so we got a copy of the game in at work now...and I totally understand what you guys mean now.  I only played for about 30 minutes, but still, I couldn't get a single damn submission to work.  I kept getting into a full mount and knocking them out instead.