I'll kick start some discussion. Are Arsenal title hopes dashed? Will Man U hold on? Will Chelsea overtake them? Will Avram Grant keep his job, or does he have to win one of the two remaining titles or both? What about Rafa?
Yes, yes, no, has to win one, needs a deep CL run and/or a strong finish for third in the league... would be the short answer in my opinion. But I think we all know that anything can happen. Now for the long answers:
This season has shown that Arsenal have tremendous quality in their starting lineup, quality that can beat any team in the world. However, what they're significantly lacking is depth. If Wenger were Rafa Benitez, this would have been revealed earlier in the season, but as it is, his worn out first team are breaking down at the finish line instead. It also doesn't help that two of their most skilled players (RVP, Rosicky) are made of glass. Part of the game is being able to stay fit, and that's one skill neither one has shown. Critics have singled out Gallas and Adebayor for special treatment of late, but a) Arsenal wouldn't have made such a great first-half run if not for those two, and b) who else can Wenger turn to in big matches? There are no good second options. Gunners like to say "Arsene knows" whenever someone questions le Professor's judgment, but it's starting to look like Arsene doesn't know when to spend the money he has.* If they can't beat Liverpool at home, another finish in fourth isn't out of the question.
Meanwhile, United have shown that they have phenomenal reserves to call upon. It's especially apparent in midfield and attacking options, where Sir Alex has a veritable embarrassment of riches. Carrick not getting it done? Bring on the veteran Scholes. Ronaldo need a rest? Let Nani take over for a bit. Tevez hurt? Go get (finally healthy) Saha or let Rooney work the line alone for a day. It's a phenomenal team, and every time I watch them play I wonder how they've ever lost. But lost they have, and the odds say they'll do it again before the year is out. So will everyone else, though, and that's why they'll win the title. (Indeed, its difficult to see their current or potential opponents in the Champions League knocking them out, and if I were a betting man, I'd mark them down for that one as well.)
Chelsea don't have the same quality as United, but they do have some good depth of their own. A fine example of this was their most recent win over Arsenal; despite the ungrateful crowd's chants of "you don't know what you're doing" and "Jose Mourinho," Avram Grant made some excellent tactical substitutions, bringing on Belletti and Anelka (who set up both goals). However, final responsibility for victory has to be laid at the feet of one Didier Drogba, who torched the Arsenal defense for two (ahem, the first had a whiff of offside, and that's all I'll say about that). Really, aside from this last match, Avram's squad have been crapping the bed in big matches, and unless he can muscle them past United and/or win the Champions League, I see them looking for a new manager. Basically, that's me saying they'll have a new manager.
Ah, Rafa. This one is clearly a mystery to me. I was certain he would get the ax during a string of lackluster results and turmoil amidst the ownership back in January, but that didn't happen. And until this last weekend, his team were playing like worldbeaters. Old Trafford is a tough place to play, it's unclear if Mascherano was deserving of two yellows (shut your mouth, you fool!), but getting torched for three like that isn't a good sign. My prediction? Arsenal has become the key for him. If he can overtake them in the league and knock them out of the Champions League, his job is safe. If not, all bets are off.
*Maybe he's learned his lesson. This is very uncharacteristic.
Arsene Wenger cobbled together starting lineups with spit and duct tape and Denilson and somehow the team dragged its ass over the finish line in third or fourth.