Since I don't know the inner workings of LR, I will give you the 'techie' version.
The slowest part of a computer is the network connection, so anything done through a network will be the first point to check. For example, I store my images on a networked 2TB Buffalo Raid server. The difference between G band wireless, 1'/1'' LANs and 1gb LAN's are huge. Using 1gb routers and network connections will speed things up quickly.
The second slowest part is the disk drive. We now have standard IDE drives (I will use IDE to include all enhanced IDE types), USB, Firewire, SCSI (scuzzie) and SATA. Yes, there are others like CF drives and USB keys, etc., but my guess is those won't be used for a working catalog). SATA is now the fastest access between the computer and the hard drive, internally. There are also enough advances that typically the enhanced IDE drives are about equal to SCSI drives. Newer laptops are starting to use SATA and this is what I would recommend as an internal drive. USB and Firewire is ok and faster than a network connection, but slower than an internal SATA drive.
Next, look at the type of hard drive and compare two properties: speed and cache. Speeds are the rate at which the hard drive spins. Compare this to the old records. The faster it spins, the faster the music, the slower it spins the slower the music. As long as the record spins, however, you still get music. Hard drive speeds range from 54''rpm (revolutions per minute) to 15,'''rpm. Typical laptop hard drives are still 54''rpm to help prevent damage when dropped, moved, or jostled (on an airplane, for example). Some laptop speeds have moved up to 72''rpm and are still reliable. There are enhanced hard drives for desk tops that move at 1',''' and 15,''' rpm, although these used to be the standard speeds for SCSI drives. Get the fastest one you can to increase speed.
The second property of the hard drives to evaluate is the cache. The larger the cache, the more image information can be read and passed to the computer. Well, not exactly, but from a user's standpoint that is true. I said previously that the connection to from the hard drive to the computer was the second slowest part. This means it get's really busy transferring data. You don't want the hard drive to sit around and wait for that connection to free up and take more data. So, the hard drive reads all it can and sends it to a cache where it waits to send data to the computer. Cache is memory which is about the fastest part of a computer. So, get the fastest hard drive with the largest cache you can.
Now we deal with some real hard core stuff. Do you have one hard drive or several in your pc? Laptop users really only have one option and that is a single hard drive. Desktop users can easily mount multiple hard drives. If you can do this, then consider a raid implementation. RAID deals with using multiple disks to act like one disk. RAID 1 is mirroring which is two hard drives exactly alike. In the real world, RAID 1 is slow to write but a little faster to read. This is because it is making a copy of everything sent to it on the second hard drive. Reading can take place with both hard drives, however, and speed us up a little (not twice as fast though, as you might think). The best speed up on read time is RAID ' where you have three disk drives that are striped. This means out of every 'file' you have parts on all three disk drives. This is fast read and write. You are using three drives based on their speeds to send data to one, when it's cache is full, move to the next to give the first time to write and so on. This gives you the fastest throughput getting data in and out of disk drives. RAID 5 is similar although there is a little extra data copied so that if a disk fails, you haven't lost any data. RAID 5 is a little slower than RAID 1 (mirrored), but much faster than RAID ' (striped). However, the speed tradeoff of RAID 5 is not much considering you have the safety of recovering when a single disk goes down.
Next would probably be the speed of your motherboard. It used to be we would all get a computer and then keep updating the processor going faster and faster. What we didn't get much of was an increase in the motherboard speed. Now you see speeds ranging from 1''mhz to 2''mhz and beyond. Buy the fastest motherboard you can get. This is like the hard disk connection, it moves data between your screen, keyboard, printer, disk drive, CPU and network. Everything goes through the motherboard at some time, so fast is best.
Then it could be a toss up between CPU speed, memory and video cards. Yes, remember that you have to put the image on the screen and a slow plain jane video card will slow down that image getting shown on the screen. I think the best bang for your buck is to increase all three of these things little by little. The fastest CPU with only 512mb in memory would be slower than a mid speed CPU with 2mb of memory. I would recommend getting as close to a 3ghz processor as you can, with twin processors (dual core) a real plus. Pay attention to the cache on these as well with a preference towards 1mb caches on the processor. Then slam as much memory as you can in your computer. 2gb is good, 4gb is great and more is better. Budgets get cramped fast in the memory department. Then splurge for a middle of the road video card that has more than 64mb or 128mb of memory. More memory typically means more colors on a bigger monitor.
You do have a big monitor don't you? Two? Even better, I am jealous!
I know this is a lot of 'stuff', but these are the areas you can really speed up processing and that's what lightroom really is.
My personal setup is this: PC, 3.2ghz dual core processors with 2mb of cache (1mb each), 4gb of memory, 512mb of viedo memory and a 2TB RAID 5 network disk drive. I chose to allow the speed decrease by using a 1gb network over an internal drive for backup reasons only.
Good luck!
