Wait - but no too long!
I say yes, waiting is worth it. Modern culture has made it incredibly hard as waiting seems unnatural to most people and to me the answer is that we should get married earlier - but that of course comes with its own problems! Serioulsy though, I think that's the only logical conclusion. There should be no long term Christian relationships that aren't heading for marriage. If you've been with somebody for, say a year (a somewhat arbritrary timescale admittedly!) and there are no marriage plans then the relationship is perhaps not right - at least, not at that time.
'Long' Christian relationships introduce sexual tension that isn't healthy. If you aren't able to commit, ask yourself why. If it's the relationship, end it. If it's you, don't enter relationships until you're ready to commit.
I've learned this the hard way and I wouldn't wish my experiences on anybody. My partner wasn't ready to commit to marriage, so because I loved them I was patient and waited. Close to 10 years later we're finally planning to get married. Recently though, I discovered that the inevitable sexual tension was being diverted elsewhere - because apparently, so as long as it wasn't 'real' sex, a) it didn't count and b) because those people weren't Christians that held the same values (and therfore weren't marriage material), it didn't matter too much what happened because it wasn't leading anywhere so didn't need a solid grounding. I do understand how this happened but it doesn't make it any less painful.
The hardest bit is that because we both agreed we'd wait, my partner is hugely embarassmed about admitting what has happened with others. So can only seem to get as far as admitting that they fell short of the way they'd like to have behaved but is adamant that they didn't have sex. So I have no idea what they did actually do. I'm sure we both know that they should be telling the truth now but they're finding it really hard to do it, so instead they just claim they can't remember (because it wasn't important or significant). Personally, I find that hard to believe. I think that when you choose to wait (which is not normal by today's standards), any sexual activity is a big deal, so it's unlikely you'd forget what you'd done. I think they're embarrassed, sorry for the hurt they've caused and ashamed that they've behaved one way with the person they love and another with various others that weren't even important to them. The end result is that they can't manage to tell the truth. Such a shame because despite the hurt, I could forgive the mistakes - we're all human after all but not telling the truth underminnes trust and I find it hard to forgive that or accept that it's wise to carry on with marriage plans in the circumstances. I hope they'll realise that soon.
In my view though, irrespective of any individual's mistakes here, the whole situation has been largely caused by the pressure of choosing no sex outside of marriage and then choosing to wait a similar length of time to a non-Christian couple before getting marrried. That's bound to have caused masive strain. If I'm honest, I've been tempted to break the rules myself. If you're not called to celibacy, it's not natural to spend so long in a non-sexual relationship.
So, in short, I believe waiting is the right thing. Save yourself for the one you want to spend your life with but do it within the whole Christian life. Be excluscive to one another, don't have shadows in your history. Don't try and mix worldy standards with Christian ideals. It doesn't work. And remember, once you've crossed a line once, it gets easier to do it again and harder to explain to somebody else why you choose not to cross that line again. I've learned a hard lesson, I hope somebody else learns from my mistake. (apologies for length, it's quite an important subject in my life right now!)