You aren't really asking a question that hasn't been asked, and answered, 1,000 times over already. There are pros and cons to every type of technology out there, but the bottom line is that most displays have a life expectancy that exceeds 10 years for normal use. Which is in line with what you have received from regular CRT displays over the years.
That is, the electronics inside are more likely to fail before the display itself fails.
But, within every product category you have manufacturers that do a lot better job with their displays than other companies do. At about 50" or so, the Sony SXRD rear projection units look great, aren't terribly expensive, and the newest lineup is 1080p and accepts 1080p. A big plus looking forward.
In my opinion, the only time to use a flat panel display, like plasma or LCD is when you really have limited space and coming off the wall 18" is to much space. They are great for bedrooms and other locations where floor space may be valuable, but I will never understand when people get a plasma or LCD, then put it on a table which is dedicated for their A/V gear. In my experience, most plasmas and LCDs do not look as good as rear projection DLP, LCD, and LCoS units.
DLP, LCD, and LCoS all are rear projection (or front projection) technologies that use a lamp. The lamp is almost always user replacable and can last you several years before it needs to be replaced. When you replace it, yourself, you basically have what amounts to a brand new display. That is, until electronics inside fail.