I'm not an event videographer, but if I was going to buy into HD here it was I would be thinking about:
1. The Format - There's a whole bunch -- AVCHD, HDV, DVCPro HD, and XDCam HD, to name a few. Those are the formats I see most often. What's the difference between all of them? AVCHD and HDV are very compressed; AVCHD is more compressed than HDV. That causes problems if you are going to be doing any wild effects and/or compositing. DVCProHD and XDCam HD are less compressed. DVCPro HD is made by Panasonic and XDCam HD is made by Sony, although I've read that JVC will also be supporting that codec soon.
2. Frame rates / resolution - The resolutions are 1920X1080 and 1280X720. They can both record in 24p, 30p, 60i, and 60p, but not all cameras record all the resolutions and frame rates. 108060p is harder to find in the less costly prosumer models.Â
Also, some cameras record 1440X1080 and stretch the images to cover 1920X1080. Others record true 1920X1080. Â
3. Media - When I go HD, I want to implement a tapeless workflow. Tape is nice because you know your footage is there and initially it's cheaper; however, P2 cards are proven to be very stable and cut capture time down by a lot. Actually, if you decide to record to tape, then you need an HD deck too, unless you want to wear out your camera. So going tapeless may actually be cheaper depending on how many cards you get.
4. What is being shot - If you shoot events, chances are your days will be long and you won't have a chance to offload footage from a P2 card or SxS card to a laptop as your day progresses. So the more compressed formats like AVCHD and HDV may be the formats you want to record if you know you aren't going to be doing any compositing. If you shoot in controlled environtments and you have time to offload footage from cards to laptops, DVCPro HD and  XDCam HD may be the way to go.Â
5. Input/output - I always want XLR connections. If I wanted to record uncompressed video, I would want HD-SDI outputs too.