Hi Steve, I'm not an official expert, but I do dabble with dryer vents both for fun (weird, I know) and in my line of work (plumbing, air, electric).
I hope these help:
1) 90 degree bends are pretty bad to have because they restrict air flow. What happens is that each 90 is equivalent to adding about 5ft of running length to the tube. I am realistic that you may not be able to remove the 90's, but - if possible - making things straighter will make 'em better.
2) I recently cleaned out our dryer vent with this thing off of Amazon. And - WOW - it was worth it's weight in gold. It was actually fun doing it and it did a killer job.
http://www.amazon.com/Gardus-RLE202-LintEater-10-P...
3) I'm a little unsure about the use of PVC for the dryer vent. And, in researching it, I found this little tidbit. Given that we found it on the internet, it is - by no means - the gospel. But it seemed sort of legit. "PVC pipe is fantastic for many different applications, and it is even sometimes used for duct and venting applications. BUT there are a few reasons why PVC pipe is not a great choice for dryer vents. For one, PVC has a rather low maximum operating temperature. All PVC pipe and fittings have a max operating temp of 140 degrees Fahrenheit. Now think about how hot your dryer gets. All that hot air and moisture running through the pipe for years is bound to do some damage. Second, PVC pipe is notorious for creating static electricity. Anyone who has ever cut PVC pipe with a saw can attest to this (the shavings cling to the pipe like crazy). That penchant for static mixed with the hot lint that collects in dryer vents is a recipe for disaster. Third, using PVC to vent a dryer is a violation according to most residential building codes. Save yourself the stress / possible future agony and do it to code."
4) Lastly, if you start making alterations, I don't advise using Duct Tape. You actually need to use a tape that can stand up to the hot temperatures (I think it's called foil tape).
http://www.amazon.com/3M-High-Temperature-Flue-15-...
I hope that helps some, sir!
Brian