Laszlo is a "big" thing in the Rich Internet Application development platform. The advantages it has springs from the very fact that ramp up and development using the platform is quick. However, drawing from my experience, I seemed to have noticed that the code quickly gets out of control.
Despite good practices and informed design decisions, there are times when the responsiveness goes downhill. I have seen projects where the initial performance was top notch,but as the developers continue chuck functionality at the code base, project managers tend to get edgy over the interactivity and maintainability of the code.
In addition, the size of the SWF file finally obtained after the final compilation seems to be large enough not to serve on one request. Most applications would allow lazy loading of parts of the SWF that would be accessed later.Though Laszlo provides the 'initstage' attribute, the attribute only serves to initialize the properties of the view (that is subsequently compiled into a MovieClip). The size monster still persists, resulting in slower response times for huge SWFs that Laszlo generates.
Thinking logically, the reason that this is a problem with Laszlo and not HTML is that in case of HTML (even if it is AJAX driven), the entire web application is not loaded at one go. People tend to split up the page, and then employ lazy loading if required. Technically, it is not impossible to do with Laszlo either. Being based on ECMA Script, Flash, and hence Laszlo, do support the eval and 'LoadMovie' functions. I have noticed that two Flash Runtimes with smaller SWFs loaded perform better that one Flash Runtime with a big SWF file. Also, may be Laszlo can natively support dynamic loading of content so as to keep the size of the SWF small enough.
This could be better than multiple movies as Laszlo comes with a tag of about 21K of LFC bundled with every SWF that it generates. If Laszlo could natively allow sharing these foundation classes across multiple SWFs on the same page, the download size could be a lot better.