I'd be more forgiving of Lion if it could play even one movie on my Macbook pro without occasionally going into frame-dropping VM-swapping. There's no question that my hand-built BeOS box, 15 years ago, had a far snappier userland experience.
I'm running Lion too. If you have repeatable problems, there should be some specific source for it. Tried "Activity Monitor" when it occurs?
Common problems can be: Spotlight doing indexing at the time, Flash fucking around, too little available hard drive space (less than 5GB), some rogue app, etc.
MBP 2007, 2GB RAM. I have now open: Chrome with 7 tabs, Sublime Text, Terminal (2 tabs, one SSH), Mail, iA Writer, Adium, iTunes, TunnelBlick VPN, Photoshop, Transmit, Dropbox, Alfred, Little Snitch and VLC and the movie plays just fine. I use either VLC or MPlayerX though, very rarely QuickTime w Perian.
Now, some people open 50 tabs and think that the browser should automagically handle them all, with 20 instances of Flash running in videos and apps, etc. Not so. VMs are also very resource hungry.
That said, the laptop is noticeably slower than my 4GB / i7 iMac, but not to the point it swaps --unless I start my 1GB linux VM (VMWare).
I have Lion, on a 2010 MBP, and I have Activity Monitor open ALL THE TIME.
On Snow Leopard, I found what you say to be true. On Lion, either the mysterious process is eluding me, or it is just much slower. I do development and I can tell you that the iPhone Simulator is a frequent culprit, VirtualBox is also rough (but if I ssh in to my virtual machines rather than use the GUI it's fine), also the Time Machine daemon trying to backup causes things to slow down (even when not plugged in to a disk), but even after that performance is downright crap compared to Snow Leopard.
If you have any idea what my specific source could be I'd be thrilled to hear it. Frequently at the top of my Activity Monitor is WindowServer and kernel_task, except when compiling or other fun things. Even when the interface is locking up I can't find anything fun.
The VirtualBox caught my eye... I loved using VirtualBox for a while. It's free. It basically works. It's free. Oh yeah, and it's free.
Recently, work sprung for a Parallels license for me. Yikes, I pity my past self for putting up with all the VB issues because it was free. Just little things like playing nicely with the app/spaces switch key combos, lack of crashes, and performance make me really regret wasting all those mental cycles on VB. Don't get me wrong, having a free x86 VM is wonderful and the VB developers deserve kudos galore... but I reminded myself that my time and sanity are worth a few bucks here and there.
Do you by any chance have one or more external hard drives attached? I've been having a lot of lock-up issues while I have six of them connected (through a hub) to a MacBook Pro from 2011 running Lion. It looks like this (also shows it dropping to normal levels instantly):
There's no process running wild from what I can see in the Activity Monitor, but it appears to happen a lot less frequently or not at all when I don't have my external hard drives attached.
No external hard drives attached, except when I remember to back up my machine (I frequently, but not always, plug it in when it is on my desk, but it is just for Time Machine).
Also, unless I am running heavy CPU things (XCode, VirtualBox machines, etc), I usually don't get a lot of CPU time like that.
step 1. go into /Library/Quicktime and move ALL the .component files out of there.
step 2. Go into ~/Library/Quicktime and move ALL the .component files out of there.
step 3. (re)-install perian
step 4. Try playing a movie that usually craps out.
One of the annoying things about Mac OSX is that a rogue codec can mess up ALL media playing activities on the computer- so when you encounter problems, I've found the most successful strategy is to figure out which codec is messing things up.
OK, I don't use VirtualBox, for performance reasons I use VMWare Fusion. Even with this, I find, as you, that using GUI on the VM slows the Mac much more than ssh'ing to the VM. So, the VM is a serious culprit. Certainly, if I have the VM running, I expect some slowdown and occasional swapping -- basically it means I just gave up 1 GB or memory to the VM (out of 2) plus tons of I/O scheduled by a different OS within my OS.
Other than that, I also don't run Time Machine at all -- I use Carbon Copy Cloner or Super Duper to make incremental and/or bootable backups every week or so. With iCloud, Dropbox etc for the important day to day documents, I don't see much need for Time Machine anymore.
So those would be two places to look at.
Besides those, you can try running some DTrace scripts for a more detailed look when your system starts to crap out.
