As per title, a minor suggestion:
Please let the modpack author indicate what version their modpack is built for, and show that when browsing the modpacks on the site, perhaps next to the created/last updated date (and possibly also allow the user to search/filter by minecraft version when browsing modpacks). This perhaps could also be displayed in the launcher, either in a corner of a pack's thumbnail, or in a corner of the main view when you've selected the pack. This is independent of the large description that authors can give for their pack, as - in browsing the top couple of packs - few authors even bother to mention what version of MC their pack is built for.
I know this doesn't sound like a big deal, since the launcher can handle the minecraft "versioning" itself, but it can be helpful if you want to try something completely new and different and don't want to go back to an older version. For example, I'd prefer to play MC 1.4.7, but I can't tell at a glance whether a mod pack is for 1.4.7. or 1.3.2 or 1.2.5 (or whatever the previous 'major' version was that mods built for prior to 1.4.7; I know Tekkit Classic is for 1.2.5, for example). Or if, for example, I'd want to find a modpack built for 1.5pre.
Also, if you could add a button on the launcher to download a mod without necessarily launching minecraft immediately afterward, I feel that would be helpful. When I was updating to tekkit lite earlier, I messed up a couple times trying to get optifine to work (mostly loading it to the wrong jar or using the wrong version of optifine), so every time I went to delete the jar to start over I had to run minecraft again. Obviously this isn't a big deal - in my case we're probably talking about 1 or 2 minutes tops of unnecessarily loading - but still seems like a useful utility. (I Do apologize if this option already exists somewhere that I've simply missed. I expected Reset Pack to do this but I guess it only applies when you go to launch the game?)