I'm not really wanting to have to learn a new app but I feel I'll soon be beyond what iPhoto can offer...I'm playing with the aperture trial at the moment and it seems more what I like interface wise...I'm not trying to get into the whole Aperture vs LR debate as yet, but inquiring as to others transition from iPhoto.
Silver, good luck trying not to stir the A vs LR pot. Also, it seems that there are some shills who are always pushing LR (not saying that is happening here). Not sure what your specs are, or what version you are using... but with 8k in your library, you should not be lagging yet. You might want to make sure that your IPhoto trash is emptied... other than that, your IP photo library might be corrupted. Usually there are other symptoms and odd behavior that would tip you off. Read this for how to rebuild it:
http://support.apple.com/kb/HT2638
I am one who uses BOTH Aperture & iPhoto (professionally). I transitioned away from Portfolio, which I used for archiving our image library. I hated Portfolio... it was SLOW, cumbersome, and only offered 2 tiny preview sizes... whereas IP could scale the images to any preview size, and offered some basic, imaging adjustments. IP had the slight lead interface-wise and was a bit more intuitive. Some of A's logic might be a bit frustrating, and it always defaults back to the "top" of the image archive when switching between albums, and when reopening the ap (IP usually remembers where you left off). A is due (overdue) for a refresh, but even as it is it is a wonderful ap.
I maintain a pretty big (60k+) library, and have moved vast amounts of my imaging away from pshop. 90% of my imaging is done within Aperture these days, and the only thing I gush more about than Aperture, is the NIK software suite from Nikon. The non-destructive, size independent, workflow is a godsend. The only thing I am missing is CMYK support, and layers & type... but that is no biggie, as I can just control click to edit/work within Pshop.
Lastly, I could be mistaken, but I think you can apply more than 1 keyword to your smart-albums, at least after you have created them. Have you tried selecting the images you want to keyword...going to the keyword hud and select the keywords you want to apply. Then drag the keywords across to the image browser and the selected images should have the keyword.
I run both Aperture & iPhoto from a first gen 24" iMac with 3gb ram. It creaks here and there, but my library is pretty big... it runs fine though. I will be upgrading to a 27" with 16 or 32gb pretty soon... hopefully just about the time Aperture 3.0 is out.
michael