My experience so far is that R8 more stable than R7. I rarely crash, but do almost nothing with surfaces, and only simple sheetmetal. I have also seen a major improvement in .dwg output from R8 and compatibility. R8 also will keep the link between autocad drawing and Inventor part, so if you change the model, the autocad drawing will update.
I test drove SWX for about 6 weeks and went back to inventor. I found ease of learning just the opposite as Alan (it really depends on what you learned first, and how you work). I found SWX having major problems with solving constraint (mate) issues, and I found it to be more difficult to mate things together. (just my experience)
As far as stability, spend a little time on the solidworks section of this forum and look at the issues that they are having with 2004 (I think they are on SP3 since september)
This issue has been (and will be) debated at great length, and my take is:
SWX is better with sheetmetal, and surfaces, and drawings are somewhat better, has e-drawings (which have their own limitations), photo-rendering, and a very simple FEA program built in.
Inventor is easier to use and learn, performs better with many large assemblies (not all types), dwg output and import is improving, drawing performance is much better with R8, I found much more standard content (parts) for download, more free add-ons, the Adesk newsgroup will get you technical help very fast (from other users), you get the most recent autocad and MDT versions with Inventor, if you have MDT--Inventor is very inexpensive.
Both companies seem pretty sleazy, but SWX seems worse IMO. Subscription costs are similar. You see rumors about Desault/catia/SWX but that is just speculation. Get eval's of both, and test them, and keep talking to other users. Not an easy decision.
Some good Inventor sites:
(with lots of good links to Kent Keller's site and others)also has some great FREE tutorials
(for major parts content)