The paper specifications look similar. The Zoom has 4 microphones, making it configurable for different pick-up patterns, including 4 channel surround. The Olympus comes with 2GB flash memory as standard, whereas the Zoom has only 512MB (upgraded mine to 2 GB for £17 GBP). The Olympus is a fair bit more expensive than the Zoom. The build quality of the zoom looks a bit delicate (all plastic), but has survived being dropped onto a carpeted concrete floor from about 1.5 meters, without any damage (I do NOT recommend trying that
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I mostly use my Zoom H2 for recording music (a very wide variety -including solo violin, vocals, piano, full rock band) and have also used it for recording speech.
Neither of them would be suitable for close vocal microphones (wrong sort of microphones), but either of them are likely to do a good job with music or interviews.
Other recorders in a similar price range are the Edirol R-09 HR and the Sony PCM-D50. Of these 4, the Zoom is the least expensive by quite a long mark (Samson/Zoom have an excellent reputation for high quality/low price).
I chose the Zoom H2 as I was very impressed with the recording quality, the ease of use, and value for money.
Professional broadcast quality machines would be things like a Nagra, or a Fostex FR-2, both of which are considerably more expensive, but you are paying for superlative sound quality, build quality, reliability, environmental robustness, etc. If I was going on a recording expedition to the inner reaches of the Congo, I think that I would rather be relying on one of these rather than either the Zoom or the Olympus.
There's a few ideas for you there - I guess you will just have to have a look at which one of them you like and make a decision.