Yes, I am using Windows Defender.

I just tried going into Defender's setup and excluding the Start Menu folder and the Start Menu\Programs folder biut it made no difference. I think it does not exclude subfolders, and it would take forever to exclude each subfolder.

I tried turning real time protection off and that does work. Then there is only a tiny delay. So it is an interaction with Defender.

It can take almost 10 seconds for a submenu to open. It then seems to get faster but I think it also gets slower again after an interval. Odd.

To give you an idea how large my start menu is I just had a look and it has 577 files and 189 folders. So you should use a system with something like that for testing.

It is something we are investigating and I would hope for it to be improved massively in the next update.  We have an upcoming change to the tree loading code specifically aimed at overall tree load performance.

Why defender is causing this type of delay on some machines is something I cannot say as it shouldn't be and none of the other AV apps seem to have a similar problem.

Great that this issue is being addressed in Start8!  

I have been using different free AV-Programs (and Firewalls) over the years like Antivir ect. but since Win7 I switched to MSE and Defender which is in Win8 now included as Defender because it does have advantages to have sth. like this deeply included in the OS. The best primary AV is the brain anyway But having sth. supplement that by means of software helps none the less... 

Great news.

If you query the target of a link Defender decides it needs to scan the file that the link relates to.  The file itself isn't being queried by Start8, just the shortcut target.

It seems Defender then remembers it has done this and doesn't do it again until the next reboot.

I have the same issue as RichardBeal in that opening the Games folder from the right-hand side of the Start menu, which is set up as a menu with over 90 games in it, or the All Programs > Games or 3Planetsoft screensaver folder, which has some 20+ sub-folders, freezes Start8 for upto a minute on my system. The more sub-folders or shortcuts it has the longer the freeze lasts. Once they've been accessed then they open instantly on subsequent attempts but the sluggishness returns once I reboot or turn off my PC (which I do regularly as I never leave my PC on when I'm not using it). I have Windows 8 Pro 64-bit installed and I'm running it off a 256 GB Crucial m4 SSD with 134 GB free.

I found that when I disabled Defender that the menus opened as fast as they did in Windows 7 but despite adding exclusions for the C:\User, C:\ProgramData, etc. folders as well as for *.scr and *.lnk files, as soon as I re-enable Defender the problem menus again take ages to open the first time I access them. Oddly, this issue never occurred in Windows 7 even though I was using Microsoft Security Essentials, Defender's predecessor, without any exclusions! Personally, I think Defender is a little buggy as I've seen it regularly using 13% of my CPU when I open my picture folder even though the My Pictures folder is excluded from scanning!!! Personally, I would have preferred to have kept Microsoft Security Essentials as Defender actually has fewer options and seems more like a stripped down version.

Excellent news though that this issue was being looked at and is now fixed because, that issue aside, Start8 has been working brilliantly and I've not crashes or anything like that. It can only get better once the few remaining kinks are ironed out.

That does not work. It probably appeared to work to you because once you had opened the folder once it was then fast. But reboot and you will see the problem again.

Done some tests with various free Antivirus-Solutions. Some did not install at all even though they claim to be be compatible with Win 8 (Panda Cloud); Avira claims to be not compatible yet, AVG slowed everything down to the level of the system being unusable. 

I have Avast! Free installed now and Defender disabled... I wanted to try if that also fixes various freezes with Windows Explorer - and it seems it does help. Start8-Menues are faster, though large ones still have some noticable delay. Freezes in Explorer seem to be gone, but then they appeared randomly so this may just be a temporary effect. 

I would like to add here that Avast! seems to cause severe complete freezes in my installation with the need to hard reset, so I have not found a smoothly working free alternative to Defender yet. 

So I switched back to Defender and with the new beta of Start8 the Folder open "near instantly" like they are supposed to  

What I like about MSE / Defender is that it runs silently in the background but does it's job.... Most alternative solutions seem to want to emphasize their "protectiveness" by throwing all kinds of information in your way all the time...