This is a bit of an odd film: it's a romantic comedy, but the two lead characters are pretty unlikeable, so I didn't really care what happened to them at all. On the other hand, the supporting cast were excellent, and I recognise several of them from other films (e.g. the sidekick from National Treasure). They had some very funny scenes, and their own subplots, i.e. their lives didn't just revolve around the (nominal) protagonists. All in all, I enjoyed it, but I'd like to see a director's cut where they chop out all the boring bits.
Going into a bit more depth about the film, and the real-world implications, I need to invoke a spoiler warning.
The basic premise is that Tripp (lead male character) has lived with his parents all his life, and it's a pretty good deal for him: his mother still cooks breakfast for him, and takes care of his laundry. However, his parents now think that it's time for him to move out, so they hire Paula to date him. She specialises in cases like this, so her plan is to build up the guy's confidence enough for him to move out and build his own life. ("For many young men, self-esteem develops during a romantic relationship. So, I simulate one.") However, as you'd expect from this genre of film, Tripp and Paula wind up really falling in love.
It's similar to films like Hitch and Pretty Woman, but they both work better. In Hitch, the eponymous character acts as a life coach, and his goal is to get his clients into long term relationships; however, Paula fully intends to dump each of her clients, so I'm not clear on how this will help their self-esteem. As for Pretty Woman, Vivian was upfront about the fact that she was a prostitute, so Edward knew what he was getting into, and it's a happy chance that things wound up working out well for them. In this film, Paula lies to Tripp right from the start (making him think that he bumped into her randomly), and when she talks to his parents she denies being a prostitute; she may not normally have sex with her clients, but she's more than just an escort, i.e. she does get physically intimate in return for money.
Another flaw in this film is that Paula isn't exclusive: she's working with several clients at a time. This is how Tripp's friends figure out what's going on, when they see her on a date with a Star Wars fan. (The film doesn't show what happens to him at the end.) This seems like a poor strategy; even if people don't realise she's a "pro", they'll still see it as a betrayal. Basically, I'd describe her as a lying manipulator, leading men on while she two-times them. Tripp comes off a bit better, but not by much. In the DVD extras, the producers said that they had to choose good looking actors to offset the characters' personalities. As I said above, I think it's best to ignore the lead duo as much as possible and focus on their friends, who are much more likeable.
The main problem I have with the premise of the film is that Tripp's parents never tried the simple approach of just talking to him. It would be much easier all round if they just told him: "Son, we think it's time for you to move out and get your own place." That would avoid the whole elaborate deception.
Still, the film does raise a question: is it ok to keep living with your parents once you reach a certain age, or should you really move out? I'd say that it depends on the specific circumstances, but I don't think there's anything intrinsically wrong with staying at home. Personally, I moved out when I was 18, and I haven't been back since. I won't go into the details here; it wasn't an ideal situation, and in retrospect I think I could have handled it better, but I don't regret my decision. However, just because that was the right thing for me, it doesn't mean that everyone else should follow my example. As for the stereotypes, I don't think they have much merit. I moved out from the family home 15 years ago, and I've lived in my own flat for the last 4 years, but I've never been in a romantic relationship. By contrast, I know other people who live with parents in their 30s who have been much more "active" than me.
So, why not move out? One potential reason is disability; this could apply to the "adult child" (not capable of living alone), or it may be that they need to take care of elderly parents. Looking at fictional examples, that was the premise of Frasier (his father had been shot in the hip and needed help around the home), and in Something Positive Davan moved back home to take care of his father after Fred developed Alzheimer's. In a situation like that, I don't think anyone would feel ashamed about still living with their parents.
On a less drastic level, it may simply be the most practical approach. It's expensive to rent/buy your own place, so you can probably save money by staying at home. At the same time, if you pay rent to your parents, that will help them with their bills. Also, some people would get lonely on their own, so why not stay with people you like? In my case, I've spent several years sharing flats with university friends, but as my friends get older they tend to pair up, and want to get flats of their own. There's a related issue of "lifestyle inflation"; how many people do you know in their 40s who share a flat/house with friends? Chances are, even if your friends are single, they'll get their own place (like I have), so that reduces the pool of potential flatmates; I haven't had much luck living with strangers, so I can understand why other people would prefer to avoid that.
There's also a cultural issue: the film was made in America, but I gather that people tend to live with their parents for a lot longer in Asian countries.
Ultimately, I say live and let live. If someone lives with their parents, and they're all happy with the situation, it's not hurting anyone else so there's no call to mock them for it.